Non-Adiabatic Nuclear Dynamics

A non-adiabatic silica microfiber is proposed for displacement or strain and high temperature sensing for the first time. The spectral response of the microfiber depends on the difference of the effective refractive indices of the core and the cladding modes, which induces resonant wavelength shift against the strain and temperature. It is observed that the peak wavelength of the transmitted comb spectrum is blue-shifted against displacement at a rate of 4.2 pm/m. The temperature sensitivity of the device was measured to be 12.1 pm/ • C with an excellent linearity for temperature measurement up to 800 • C.

This paper discovers molecular symmetry (MS) properties of conical intersections (CIs) and the related nonadiabatic coupling terms (NACTs) in molecules which allow large amplitude motions such as torsion, in the frame of the relevant molecular symmetry group, focusing on groups with one-dimensional (1-d) irreducible representations (IREPs). If one employs corresponding MS-adapted nuclear coordinates, the NACTs can be classified according to those IREPs. The assignment is supported by theorems which relate the IREPs of different NACTs to each other, and by properties of the NACTs related to the CIs. For example, planar contour integrals of the NACTs evaluated along loops around the individual CIs are equal to +π or -π, depending on the IREP-adapted signs of the NACTs. The + orsigns for the contour integrals may also be used to define the "charges" and IREPs of the CIs. We derive various general molecular symmetry properties of the related NACTs and CIs. These provide useful applications; e.g., the discovery of an individual CI allows one to generate, by means of all molecular symmetry operations, the complete set of CIs at different symmetry-related locations. Also, we show that the seams of CIs with different IREPs may have different topologies in a specific plane of MS-adapted coordinates. Moreover, the IREPs impose symmetrical nodes of the NACTs, and this may support their calculations by quantum chemical ab initio methods, even far away from the CIs. The general approach is demonstrated by application to an example. Specifically, we investigate the CIs and NACTs of cyclopenta-2,4-dienimine (C 5 H 4 NH) which has C 2V (M) molecular symmetry with 1-d IREPs. The results are confirmed by quantum chemical calculations, starting from the location of a CI based on the Longuet-Higgins phase change theorem, until a proof of self-consistency, i.e., the related symmetryadapted NACTs fulfill quantization rules which have been derived in [Baer, M.

This paper presents a new 10T SRAM cell that has enhanced read speed along with good read and write stability. While the read access time of the proposed cell is 0.72x and 0.83x smaller as compared to the two most popular 10T SRAM cells at 500C; the read SNM is 1.16x and 1.05x higher compared to existing 10T cells. Though the read-write power of the proposed cell is higher with respect to the existing 10T cells; nevertheless, it consumes lower power as compared to the conventional 6T cell. Layout using 45nm technology rule shows that the proposed cell consumes 15 % smaller area as compared to popular Schmitt-trigger based 10T SRAM cell. Also, the results of Monte-Carlo simulation show that the proposed cell is more robust against process variations. Therefore, the proposed 10T SRAM cell can be used where the speed and robustness are the primary requirements.

We analyze perturbed version of the complex Toda chain (CTC) in an attempt to describe the adiabatic N -soliton train interactions of the perturbed nonlinear Schrödinger equation (NLS). We study perturbations with weak quadratic and periodic external potentials by both analytical and numerical means. The perturbed CTC adequately models the N -soliton train dynamics for both types of potentials. As an application of the developed theory we consider the dynamics of a train of matter -wave solitons confined in a parabolic trap and optical lattice, as well as tilted periodic potentials.

The approach to calculate improved, two-state, adiabatic-todiabatic transformation angles (also known as mixing angles), presented before (see Das et al., J Chem Phys 2010, 133, 084107), was used here while studying the F þ H 2 system. However, this study is characterized by two new features: (a) it is the first of its kind in which is studied the interplay between Renner-Teller (RT) and Jahn-Teller (JT) nonadiabatic coupling terms (NACT); (b) it is the first of its kind in which is reported the effect of an upper singular RT-NACT on a lower two-state (JT) mixing angle. The fact that the upper NACT is singular (it is shown to be a quasi-Dirac d-function) enables a semi-analytical solution for this perturbed mixing angle. The present treatment, performed for the F þ H 2 system, revealed the existence of a novel parameter, g, the Jahn-Renner coupling parameter (JRCP), which yields, in an unambiguous way, the right intensity of the RT coupling (as resembled, in this case, by the quasi-Dirac d-function) responsible for the fact that the final end-of-the contour angle (identified with the Berry phase) is properly quantized. This study implies that the numerical value of this parameter is a pure number (independent of the molecular system): g ¼ 2 ffiffi ffi 2 p =p (¼ 0.9003) and that there is a good possibility that this value is a novel characteristic molecular constant for a certain class of tri-atomic systems. V

This paper examines the doublet potential energy surfaces (PESs) governing the NH+ (Hz)-NH: (H) reaction by combining ab initio calculations of the PES with a model Hamiltonian. It appears that in Czv collisions, the deep ground-state minimum is separated from the reactants by a barrier of about 1.2 eV. In the reuon around the barrier, several PESs exhibit crossings which become avoided for lower symmetry. Thus, in this region low energy paths between reactants and products can arise which do not necessarily sample the deep minimum of the ground state. These paths, together with possible non-adiabatic transitions, can therefore account for the experimentally observed behaviour of the reaction.

A double-sheeted double many-body expansion potential energy surface is reported for the coupled 1 2 A′/ 2 2 A′ states of HN 2 by fitting about 6000 ab initio energies. All crossing seams are described to their full extent on the basis of converged results. The lowest adiabatic sheet is fitted with a rmsd of 0.8 kcal mol-1 with respect to the calculated energies up to 100 kcal mol-1 above the absolute minimum, and the topology of the first excited-state investigated with the aid of the upper adiabatic sheet. A new scheme that overcomes obstacles in previous diabatization methods for modeling global double-sheeted potential energy surfaces is also reported. The novel approach uses a global diabatization angle which allows the diabats to mimic both the crossing seams and atom-diatom dissociation limits.

We report calculations of the vibrational spectrum of HD 2 in its first-excited electronic state by using a coordinate-transformation technique. The implications of the geometric phase (GP) effect in the spectrum have been investigated. The results show that the lowest 45 vibrational levels calculated using the traditional Longuet-Higgins phase (φ/2, where φ is the pseudorotation angle) are in good agreement with those obtained by using a single-surface generalized Born-Oppenheimer equation previously reported by the authors.

So far, most studies of the geometric phase effect have presumed that the phase is path-independent; hence, one must supply another restriction concerning the boundary condition on the nuclear wave functions when dealing with nonsymmetric isotopomers of X 3 systems. We report calculations of the vibrational spectra of HD 2 using a recently proposed generalized Born-Oppenheimer (GBO) formalism. The calculations demonstrate that there are significant differences between the results calculated from the present GBO method and those based on the preceding presumption.

We discuss the singularities which arise in the Hamiltonian operator at a crossing seam involving two potential energy surfaces of the same global symmetry. The Mead±Truhlar and our own equations are discussed and found to dier from each other, although leading to identical phases up to a constant factor and sign in the vicinity of the crossing seam. Also established are the relations which link the vector and scalar gauge potentials with the mixing angle.

Submitted for the MAR07 Meeting of The American Physical Society Non-adiabatic effects in photoelectron spectroscopy MICHAEL SCHUURMAN, DAVID YARKONY, Johns Hopkins University-Recent developments in the construction of approximately diabatic second-order Hamiltonians in the vicinity of conical intersections have been employed to study photoelectron spectra of molecules in which nonadiabatic effects are preeminent. Our current approach explicitly includes all non-adiabatic coupling terms through second order, while requiring ab initio data at only (N[int] + 3) or (N[int] + 15) points for two and three-state intersections, respectively, where N[int] is the number of internal coordinates. This scaling allows very accurate wave functions to be used. Since the Hamiltonian is determined at a point of conical intersection, the method is "selfpolicing" in that the ability of the resultant surfaces to reproduce the vicinity of seams of intersection, as well as energy minima and the Franck-Condon region, is easily verified. We will report photoelectron spectra determined from these diabatic representations employing a harmonic oscillator basis and a Lanczos solver algorithm to diagonalize the resultant vibronic Hamiltonian matrices. The results of some initial applications will be discussed, with emphasis on the previously studied five membered heterogeneous ring systems, pyrazolyl (C3H3N2) and pyrrolyl (C4H4N) doublet radicals. These systems are of particular interest since they display lowlying conical intersections adjacent to both the neutral ground state geometries and the Franck-Condon region.

Nonadiabatic coupling terms between the four lowest singlet states of H 3 + were calculated ab initio. The analysis according to the criteria suggested by Baer and Alijah [Baer and Alijah, Chem. Phys. Lett. 319, 489 (2000)] shows that as many as four electronic states may be required for an accurate description of the reactions H + H 2 + (v,j) H + + H 2 (v ,j), depending on the collision energy.

3MLCT of [Ru(bpy)3](PF6) 2 (bpy : 2,2'-bipyridine) in solid state above 350 K decays via the lowest excited d-d state lying higher with a frequency of 7 × 1013 S-1 at the high-temperature limit. Crystal water of [Ru(bpy)3]Cl 2 • 6H20 lowers the energy level of an intermediate for the nonradiative decay by-2000 cm-i. Crystalline sample of [Rh(bpy)2Cl2](PF 6) at 536 K emits an unresolved phosphorescence with a fwhm of 6000 cm-1, which comes from two closely lying excited d-d states. Nonradiative decays of the lowest excited d-d state occur via the second lowest excited d-d state with a more displaced potential curve in a higher-temperature region of 350-586 K.

We study the electronic resonant states of H3 with energies above the potential energy surface of the H + 3 ground state. These resonant states are important for the dissociative recombination of H + 3 at higher collision energies, and previous studies have indicated that these resonant states exhibit a triple intersection. We introduce a complex generalization of the pseudo-Jahn-Teller model to describe these resonant states. The potential energies and the autoionization widths of the resonant states are computed with electron scattering calculations using the complex Kohn variational method, and the complex model parameters are extracted by a least-square fit to the results. This treatment results in a non-Hermitian pseudo-Jahn-Teller Hamiltonian describing the system. The nonadiabatic coupling and geometric phase are further calculated and used to characterize the enriched topology of the complex adiabatic potential energy surfaces.

Efficient photocyclization from a low-lying triplet state is reported for a photochromic dithienylperfluorocyclopentene with Ru(bpy) 3 units attached via a phenylene linker to the thiophene rings. The ring-closure reaction in the nanosecond domain is sensitized by the metal complexes. Upon photoexcitation into the lowest Ru-to-bpy 1 MLCT state followed by intersystem crossing to emitting 3 MLCT states, photoreactive 3 IL states are populated by an efficient energytransfer process. The involvement of these 3 IL states explains the quantum yield of the photocyclization, which is independent of the excitation wavelength but decreases strongly in the presence of dioxygen. This behavior differs substantially from the photocyclization of the nonemissive dithienylperfluorocyclopentene free ligand, which occurs from the lowest 1 IL state on a picosecond time scale and is insensitive to oxygen quenching. Cyclic voltammetric studies have also been performed to gain further insight into the energetics of the system. The very high photocyclization quantum yields, far above 0.5 in both cases, are ascribed to the strong steric repulsion between the bulky substituents on the dithienylperfluorocyclopentene bridge bearing the chelating bipyridine sites or the Ru(bpy) 3 moieties, forcing the system to adopt nearly exclusively the reactive antiparallel conformation. In contrast, replacement of both Ru(II) centers by Os(II) completely prevents the photocyclization reaction upon light excitation into the low-lying Os-to-bpy 1 MLCT state. The photoreaction can only be triggered by optical population of the higher lying 1 IL excited state of the central photochromic unit, but its yield is low due to efficient energy transfer to the luminescent lowest 3 MLCT state.

3MLCT of [Ru(bpy)3](PF6) 2 (bpy : 2,2'-bipyridine) in solid state above 350 K decays via the lowest excited d-d state lying higher with a frequency of 7 × 1013 S-1 at the high-temperature limit. Crystal water of [Ru(bpy)3]Cl 2 • 6H20 lowers the energy level of an intermediate for the nonradiative decay by-2000 cm-i. Crystalline sample of [Rh(bpy)2Cl2](PF 6) at 536 K emits an unresolved phosphorescence with a fwhm of 6000 cm-1, which comes from two closely lying excited d-d states. Nonradiative decays of the lowest excited d-d state occur via the second lowest excited d-d state with a more displaced potential curve in a higher-temperature region of 350-586 K.

The current decade has seen illuminating and extensive study of interplay of topological effects such as Renner-Teller and Jahn-Teller (JT) effects in small molecules. Study of such effects in HCNH molecule showed an interesting feature that for slightly bent system, a pair of JT conical interactions (CIs) appear only for certain nonplanar configuration, in contrast to its appearance in C S configuration (molecular plane) for C 2 H 2 +. Moreover, since the feature of appearance of JT-CIs in two 2 + states of HCNH in some bent configuration may be critically associated to the abundance of HNC in interstellar spaces, as advocated recently by Das and Mukhopadhyay (J. Phys. Chem. 117, 8680 (2013)), the interest in such topological studies have remained relevant. In this article we have investigated such topological effects for slightly bent N 2 H 2 + and HBNH +. Interestingly, the appearance of JT-CIs are, for HBNH + , in molecular plane while for N 2 H 2 + , in certain nonplanar configuration, in sharp contrast to the effect in the otherwise similar pair of molecular systems, C 2 H 2 + and HCNH.

Our method (parts 1-3) for estimating solvent effects on electronic spectra in media with strong solutesolvent interactions is extended to interpret the MLCT absorption spectrum of Ru2+(NH3)5-pyridine in dilute aqueous solution: it should be generally applicable to inorganic charge-transfer spectra. First, both ab initio MCSCF and INDO/S-CI methods are used to estimate the gas-phase electronic excitation energies and state charge distributions; second, Monte Carlo simulations are performed to determine the ground-state liquid structure; finally the solvent shift is evaluated based on the gas-phase charge distributions and the explicit ground state solvent structure: no arbitrarily adjustable parameters such as "cavity radii" are required. Several intermolecular potential surfaces are used to investigate the relationship between solvent shift and solvent structure, with the most reasonable structure determined by comparison with results simulated for dilute Ru2+-(m 3) 6 solution: for this complex, the inner solvent shell contained 13 water molecules which formed 18 hydrogen bonds to the ammonia ligands. The solvent shift calculated using various methods is-7500 f 1500 cm-I, implying that the gas-phase transition energy should be 32000 f 1500 cm-I, consistent, given the level of approximation used, with the INDO/S-CI and ab initio MCSCF predictions which range from 34 000 to 39 OOO cm-l. It is proposed that a method which is both practicable and reliable for calculations such as this is to use ab initio SCF ESP charges combined with Kollman's force field as the intermolecular potential during the simulations and to use INDO/S-CI charges when evaluating solvent shifts.

An extended Longuet-Higgins formalism recently utilized to obtain generalized Born-Oppenheimer equations including the geometrical phase effect has been used to study a threefold pseudo-Jahn-Teller type electronic degeneracy. The results of dynamics calculations carried out with the novel formalism are compared with Born-Oppenheimer (geometrical phase ignored), extended Born-Oppenheimer, and coupled three-state ones for the same system. The theory shows unprecedented simplicity while depicting all features.

So far, most studies of the geometric phase effect have presumed that the phase is path-independent; hence, one must supply another restriction concerning the boundary condition on the nuclear wave functions when dealing with nonsymmetric isotopomers of X 3 systems. We report calculations of the vibrational spectra of HD 2 using a recently proposed generalized Born-Oppenheimer (GBO) formalism. The calculations demonstrate that there are significant differences between the results calculated from the present GBO method and those based on the preceding presumption.

The behavior of single-surface nuclear wavefunctions in the vicinity of the conical intersection at the equilateral triangle conformations of homonuclear triatomic systems is examined analytically by using spherical coordinates which are obtained from the usual D normal mode ones. They are described by a set of three quantum numbers and shown to approach zero 3h at the conical intersection, irrespective of whether the so-called geometric phase effects are taken into consideration.

We discuss the singularities which arise in the Hamiltonian operator at a crossing seam involving two potential energy surfaces of the same global symmetry. The Mead±Truhlar and our own equations are discussed and found to dier from each other, although leading to identical phases up to a constant factor and sign in the vicinity of the crossing seam. Also established are the relations which link the vector and scalar gauge potentials with the mixing angle.

3MLCT of [Ru(bpy)3](PF6) 2 (bpy : 2,2'-bipyridine) in solid state above 350 K decays via the lowest excited d-d state lying higher with a frequency of 7 × 1013 S-1 at the high-temperature limit. Crystal water of [Ru(bpy)3]Cl 2 • 6H20 lowers the energy level of an intermediate for the nonradiative decay by-2000 cm-i. Crystalline sample of [Rh(bpy)2Cl2](PF 6) at 536 K emits an unresolved phosphorescence with a fwhm of 6000 cm-1, which comes from two closely lying excited d-d states. Nonradiative decays of the lowest excited d-d state occur via the second lowest excited d-d state with a more displaced potential curve in a higher-temperature region of 350-586 K.

When a set of three states appears strongly coupled within the set but interacts very weekly with other states of the Hilbert space, these three states form a sub-Hilbert space and thereby, one can express the non-adiabatic coupling (NAC) elements in terms of adiabatic-diabatic transformation (ADT)/mixing angles obviously representing the same sub-space It has been possible to demonstrate that those explicit forms of the NAC terms satisfy the Curl equations-the necessary conditions to ensure the adiabatic-diabatic transformation in order to remove the NAC terms (could be singular also at specific point(s) or along a seam in the configuration space) in the adiabatic representation of nuclear SE and to obtain the diabatic one with smooth functional form of coupling elements among the electronic states. While formulating the extended Born-Oppenheimer (EBO) equations [J Chem Phys 124 074101 (2006)] for the ground adiabatic state, we demonstrate the necessity for the existence of zero Curls of the NAC terms and discuss briefly about their analytical validity at and around the conical intersection Considering a three state diabatic Hamiltonian, namely, the so called induced Renner-Teller model, we calculate the NAC terms and their Curls analytically, and explore the nature of these quantities, when the three states are either degenerate at a point or approaching to form three states degeneracy at the same point.

An extended Longuet-Higgins formalism recently utilized to obtain generalized Born-Oppenheimer equations including the geometrical phase effect has been used to study a threefold pseudo-Jahn-Teller type electronic degeneracy. The results of dynamics calculations carried out with the novel formalism are compared with Born-Oppenheimer (geometrical phase ignored), extended Born-Oppenheimer, and coupled three-state ones for the same system. The theory shows unprecedented simplicity while depicting all features.

We present explicit form of non-adiabatic coupling (NAC) elements of nuclear Schroedinger equation (SE) for a coupled tri-state electronic manifold in terms of mixing angles of real electronic basis functions. If the adiabatic-diabatic transformation (ADT) angles are the mixing angles of electronic basis, ADT matrix transforms NAC terms to exactly zeros and brings diabatic form of SE. ADT and NAC matrices satisfy a curl condition and find a novel relation among the mixing angles for irrotational case. We also find that extended Born-Oppenheimer (EBO) equations have meaningful solution and can reproduce numerically exact results only when the equations are gauge invariant.

An accurate description of the complicated shape of the potential energy surface (PES) and that of the highly excited vibration states is of crucial importance for various unsolved issues in the spectroscopy and dynamics of ozone and remains a challenge for the theory. In this work a new analytical representation is proposed for the PES of the ground electronic state of the ozone molecule in the range covering the main potential well and the transition state towards the dissociation. This model accounts for particular features specific to the ozone PES for large variations of nuclear displacements along the minimum energy path. The impact of the shape of the PES near the transition state (existence of the “reef structure”) on vibration energy levels was studied for the first time. The major purpose of this work was to provide accurate theoretical predictions for ozone vibrational band centres at the energy range near the dissociation threshold, which would be helpful for understandi...

Conical intersections are degeneracies between multidimensional potential energy surfaces of molecular systems. It is well known that, besides these phenomena significantly modify the spectroscopic and dynamical properties of molecules, their presence in a molecular system has noticeable topological implications, as well. Such a consequence is the appearance of the topological or geometric phase. Conical intersections not only occur in nature but they can also be created by light. This can either be classical laser light or quantum light in an optical cavity. As a showcase example, by placing the formaldehyde (H 2 CO) molecule into a cavity, the topological properties (e.g., geometric or Berry phase) of the emerging light-induced conical intersection have been investigated for different cavity parameters and geometrical arrangements.

We report calculations of the vibrational spectrum of HD 2 in its first-excited electronic state by using a coordinate-transformation technique. The implications of the geometric phase (GP) effect in the spectrum have been investigated. The results show that the lowest 45 vibrational levels calculated using the traditional Longuet-Higgins phase (φ/2, where φ is the pseudorotation angle) are in good agreement with those obtained by using a single-surface generalized Born-Oppenheimer equation previously reported by the authors.

Synopsis A quantum-dynamical study of the fragmentation of H2O (B̃ B2) is carried out by using wave packet propagations on ab initio potential energy surfaces connected by nonadiabatic couplings assuming a FranckCondon initial wave packet from the ground state of the water molecule. The simulations indicate that a conical intersection between the B̃ B2 and à A1 states of H2O + allows the transfer of 80% of the initial wave packet within 30 fs, while the Renner-Teller coupling between the à A1 and X̃ B1 states determines the fragmentation branching rations in the ps timescale. The single ionization of water molecules by collisions with photons, electrons or ions leaves H2O + in several possible electronic states: X̃ B1, à A1 and B̃ B2. The first two states are obtained after removal of one electron from the two highest occupied molecular orbitals of H2O, and the corresponding cations do not fragment; however, the energy of the third state lies above the dissociation limits of the fir...

Synopsis A quantum-dynamical study of the fragmentation of H2O + (B 2 B2) is carried out by using wave packet propagations on ab initio potential energy surfaces connected by nonadiabatic couplings assuming a Franck-Condon initial wave packet from the ground state of the water molecule. The simulations indicate that a conical intersection between theB 2 B2 andà 2 A1 states of H2O + allows the transfer of 80% of the initial wave packet within 30 fs, while the Renner-Teller coupling between theà 2 A1 andX 2 B1 states determines the fragmentation branching rations in the ps timescale.

The nonadiabatic couplings which arise when two potential energy surfaces of a polyatomic molecule get close in energy can be classified as follows: (A) avoided crossings, (B) genuine intersections (Jahn-Teller and conical), (C) glancing intersections (Renner-Teller interactions). The characteristics of the potential energy surfaces in the adiabatic and diabatic representations are discussed for each case. The three coupling cases differ in the structure of the Hamiltonian matrix. When the latter is written in the diabatic representation, it is meaningful to retain the leading term only in its power series expansion. This gives rise to a so-called minimum-order model which is found to be surprisingly accurate (at least in a restricted zone of nuclear coordinates) when compared to the results of ab initio calculations. The characteristic features of each coupling case can only be understood in a two-dimensional configuration space, Le., when two nuclear degrees of freedom, often with different symmetry properties, are explicitly considered. A simple expression of the nonadiabatic transition probability between two electronic states can be worked out in the framework of the minimum-order models. Two-dimensional extensions of the Landau-Zener formula are obtained, which can be used to study the consequences of the anisotropic properties of the coupling. In the case of avoided crossings, only nuclear trajectories having a well-defined direction are able to bring about surface hopping, wheras there exists two active degrees of freedom for conical intersections. Hence, nonadiabatic processes which are controlled by genuine intersections are expected to take place faster than those controlled by avoided crossings.

The workability of beyond Born-Oppenheimer theory to construct diabatic potential energy surfaces (PESs) of a charge transfer atom-diatom collision process has been explored by performing scattering calculations to extract accurate integral cross sections (ICSs) and rate constants for comparison with most recent experimental quantities. We calculate non-adiabatic coupling terms among the lowest three singlet states of H3(+) system (1(1)A('), 2(1)A('), and 3(1)A(')) using MRCI level of calculation and solve the adiabatic-diabatic transformation equation to formulate the diabatic Hamiltonian matrix of the same process [S. Mukherjee et al., J. Chem. Phys. 141, 204306 (2014)] for the entire region of nuclear configuration space. The nonadiabatic effects in the D(+) + H2 reaction has been studied by implementing the coupled 3D time-dependent wave packet formalism in hyperspherical coordinates [S. Adhikari and A. J. C. Varandas, Comput. Phys. Commun. 184, 270 (2013)] with zero...

The intersection seam between the two lowest 1 A H states of ozone has been determined. The potential energy surfaces and the seam are calculated and discussed in perimetric coordinates which exhibit the full threedimensional symmetry. The seam is shown to form a closed curve which crosses the g 2v-restricted coordinate planes at six points. Three of these correspond to the previously determined intersection, the starting point of the present search. The other three correspond to highly repulsive regions on the potential energy surface where two atoms approach each other to within two-thirds of the O 2 bond length. At the former three points both states have 1 e 1 symmetry, but at the latter three points one state has 1 e 1 symmetry whereas the other has 1 f 2 symmetry. Consequently, there exist three additional branches of the intersection seam between these two states. Each of these branches lies entirely in one g 2vrestricted coordinate plane and connects to the previously discussed g s-seam at one point. The existence of a further intersection seam is established. A novel method for determining intersection points is described.

The 351.1 nm photoelectron spectrum of the 1-pyrazolide-d 3 anion has been measured. The photoelectron angular distributions indicate the presence of nearly degenerate electronic states of the 1-pyrazolyl-d 3 radical. Equation-of-motion ionization potential coupled-cluster singles and doubles ͑EOMIP-CCSD͒ calculations have been performed to study the low-lying electronic states. The calculations strongly suggest that three electronic states, energetically close to each other, are accessed in the photodetachment process. Strong interactions of the pseudo-Jahn-Teller type in each pair of the three states are evident in the calculations for the radical at the anion geometry. Model diabatic potentials of the three states have been constructed around the anion geometry in terms of the anion reduced normal coordinates up to the second order. An analytic method to parametrize the quadratic vibronic coupling ͑QVC͒ model potentials has been introduced. Parameters of the QVC model potentials have been determined from the EOMIP-CCSD and CCSD͑T͒ calculations. Simulations of the 1-pyrazolide-d 3 spectrum have been performed with the model Hamiltonian, treating all vibronic interactions amongst the three states simultaneously. The simulation reproduces the fine structure of the observed spectrum very well, revealing complicated nonadiabatic effects in the low-lying states of the radical. The ground state of the 1-pyrazolyl-d 3 radical is 2 A 2 and the electron affinity is 2.935± 0.006 eV. The first excited state is 2 B 1 with a term energy of 32± 1 meV. While the high-symmetry ͑C 2v ͒ stationary points of the X 2 A 2 and à 2 B 1 states are minima, that of the B 2 B 2 state is a saddle point as a result of the pseudo-Jahn-Teller interactions with the other two states. The topology of the adiabatic potential energy surfaces is discussed.

Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copies of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement. Date: 25 th November, Dissertation Director: Arvinder Sandhu 3 STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

A quasiclassical trajectory surface hopping (TSH) method is employed to study the O(3 P, 1 D) + SiH 4 reaction with special emphasis on the contribution of nonadiabatic path in the formation of various products. Tully's fewest switches algorithm is used to compute nonadiabatic transitions. Our calculation showed that while the H formation is the most important channel for the O(3 P) reaction with SiH 4 , the OH formation is the dominating channel for the O(1 D) reaction, at an initial collision energy of 8 kcal/mol. Comparison with a recent crossed molecular beam experiment shows qualitative agreement so as to primary product branching ratios, except for the formation of H 2 O from the O(1 D) reaction that was not detected experimentally. In addition our calculation revealed a major contribution ($50%) of the H 3 SiO + H channel from the O(3 P) + SiH 4 reaction through an addition complex H 4 SiO intermediate which was also not explored, experimentally.

We present state-selective measurements on the N H 2 + + H+ and NH+ + H+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH3, where the two photoelectrons and two cations are measured in coincidence using 3D momentum imaging. Three dication electronic states are identified to contribute to the N H 2 + + H+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold N H 2 + fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited N H 2 + fragment with roughly 1 eV of internal energy. The NH+ + H+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the N H 2 + + H+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the rela...

The complete vibrational spectrum of the HO 2 (X 2 A′′) radical, up to the H + O 2 dissociation limit, has been determined quantum mechanically on an accurate potential energy surface (PES), based on ∼15000 ab initio points at the icMRCI+Q/aug-cc-pVQZ level of theory. The vibrational states are found to be assignable at low energies but become more irregular as the energy approaches the dissociation limit. However, even at very high energies, regularity still exists, in sharp contrast to earlier results based on the double many-body expansion (DMBE) IV potential. Several Fermi resonances have been identified, and the spectrum is fit with a spectroscopic Hamiltonian. In addition, the vibrational dynamics is analyzed using a periodic orbit approach.

Sub-picosecond photo-isomerization is the major primary process of energy conversion in retinal proteins and has as such been in the focus of extensive theoretical and experimental work over the past decades. In this review article, we revisit the long-standing question as to how the protein tunes the isomerization speed and quantum yield. We focus on our recent contributions to this field, which underscore the concept of a delicate mixing of reactive and non-reactive excited states, as a result of steric properties and electrostatic interactions with the protein environment. Further avenues and new approaches are outlined * Corresponding author.

We investigate, both analytically and numerically, the quantum dynamics of a planar (2D) rigid rotor subject to suddenly switched-on or switched-off concurrent orienting and aligning interactions. We find that the time-evolution of the post-switch populations as well as of the expectation values of orientation and alignment reflects the spectral properties and the eigensurface topology of the planar pendulum eigenproblem established in our earlier work (2014 Front. Phys. 2 37, 2017 Eur. Phys. J. D 71 149). This finding opens the possibility to examine the topological properties of the eigensurfaces experimentally as well as provides the means to make use of these properties for controlling the rotor dynamics in the laboratory.

Ultrafast transient absorption spectroscopy serves to identify the 3 dd state as intermediate quencher state of the 3 MLCT luminescence in the non-luminescent ruthenium complexes [Ru(m-bpy) 3 ] 2+ (m-bpy = 6-methyl-2,2′-bipyridine) and [Ru(tm-bpy) 3 ] 2+ (tm-bpy = 4,4′,6,6′tetramethyl-2′,2′-bipyridine). For [Ru(m-bpy) 3 ] 2+ , the population of the 3 dd state from the 3 MLCT state occurs within 1.6 ps, while the return to the ground state takes 450 ps. For [Ru(tm-bpy) 3 ] 2+ , the corresponding values are 0.16 and 7.5 ps, respectively. According to DFT calculations, methyl groups added in the 6 and 6′ positions of bipyridine stabilize the 3 dd state by ∼4000 cm −1 each, compared to [Ru(bpy) 3 ] 2+ .

3MLCT of [Ru(bpy)3](PF6) 2 (bpy : 2,2'-bipyridine) in solid state above 350 K decays via the lowest excited d-d state lying higher with a frequency of 7 × 1013 S-1 at the high-temperature limit. Crystal water of [Ru(bpy)3]Cl 2 • 6H20 lowers the energy level of an intermediate for the nonradiative decay by-2000 cm-i. Crystalline sample of [Rh(bpy)2Cl2](PF 6) at 536 K emits an unresolved phosphorescence with a fwhm of 6000 cm-1, which comes from two closely lying excited d-d states. Nonradiative decays of the lowest excited d-d state occur via the second lowest excited d-d state with a more displaced potential curve in a higher-temperature region of 350-586 K.