Papers by alexander alijah
Modeling of N2+ and 14N15N+ fluorescence spectrum in comets
<p align="left"><strong>1. Introduction</strong&... more <p align="left"><strong>1. Introduction</strong></p> <p align="left">C/2016 R2 (PanSTARRS) was a surprising comet. Detected on September 7, 2016 by Pan-STARRS it showed an unusual composition when it became a bright comet at the end of 2017 and the beginning of 2018. It developed a coma at large (~6 au) heliocentric distance and observations showed that it had a highly unusual composition: no water molecules (or OH radical) could be detected, and the abundances of the usual radicals (CN, C<sub>2</sub>, C<sub>3</sub>) were unusually low, with a surprising coma composition dominated by CO, CO<sub>2</sub> and N<sub>2</sub> molecules with bright CO<sup>+</sup> and N<sub>2</sub><sup>+</sup> emission lines in the visible range. A high CO production rate of about 10<sup>29</sup> molecules s<sup>-1</sup> was measured (Biver et al. 2018; Wierzchos & Womack 2018) as well as a high CO<sub>2</sub> production rate (CO<sub>2</sub>/CO=1.1 from Opitom et al. 2019), and a high ratio N<sub>2</sub>/CO varying between 0.06 and 0.09 (Biver et al. 2018; Cochran & McKay 2018a,b; Opitom et al. 2019; Venkataramani et al. 2020).</p> <p align="left">The detection of such bright N<sub>2</sub><sup>+</sup> emission lines in this comet highlighted the necessity of a good modeling of the N<sub>2</sub><sup>+</sup> fluorescence spectrum in comets. The high-quality spectra published by Opitom et al. (2019) provided a good opportunity to test such a model. This model also permits to compute the fluorescence spectrum of the <sup>14</sup>N<sup>15</sup>N<sup>+</sup> species, leading to the possibility of future measurements of the <sup>14</sup>N/<sup>15</sup>N isotopic ratio in the N<sub>2</sub> molecules, one of the main constituant of the solar nebula.</p> <p align="left"><strong>2. Observations</strong></p> <p align="left">The spectra used for this work have been obtained with the UVES spectrograph mounted on the ESO 8.2 m UT2 telescope of the VLT. Three different observing nights have been used, corresponding to February 11, 13 and 14, 2018. One single exposure of 4800 s of integration time was obtained during each night and we used a 0.44” wide slit, providing a resolving power R~80,000. The slit length was 8” corresponding to about 14,500 km at the distance of the comet (geocentric distance of 2.4 au). The average heliocentric distance was 2.76 au. Opitom et al. (2019) describe in more details the data processing.</p> <p align="left">From the 2D spectra having a spatial extension of 30 rows, each of them corresponding to a different cometocentric distance, we extracted different 1D spectra for each night. These spectra were then averaged for similar cometocentric distances allowing a detailed comparison of these spectra at different cometocentric distances, the furthest one corresponding to 2x4 rows at the two extremities of the slit (i.e. at a cometocentric distance varying between 4800 and 6600 km).</p> <p align="left"><strong>3. Modeling the N<sub>2</sub><sup>+</sup> fluorescence spectrum</strong></p> <p align="left">We developed a new fluorescence model for modeling our observational spectra. The transition involved in this spectrum is the first negative group, i.e. the B<sup>2</sup>Σ<sub>u</sub><sup>+</sup> → X<sup>2+</sup>Σ<sub>g</sub><sup>+</sup> electronic transition with the (0,0) bandhead appearing near 3914 Å. We considered the first three vibrational levels (v = 0; 1; 2) for both X<sup>2+</sup>Σ<sub>g</sub><sup>+ </sup>and B<sup>2</sup>Σ<sub>u</sub><sup>+</sup> state, each of them with all the rotational levels from N = 0 to 40.</p> <p align="left">N<sub>2</sub><sup>+</sup> having no permanent dipole moment, the pure rotational and vibrational transitions are forbidden (or have a very low probability, through quadrupolar transitions, not taken into account in our model). For that reason it takes a long time for this species to reach its fluorescence equilibrium because it needs a few tens of absorption / emission cycles between the X<sup>2+</sup>Σ<sub>g</sub><sup>+</sup> and B<sup>2</sup>Σ<sub>u</sub><sup>+</sup> states to reach this equilibrium. A comparison of the spectrum obtained on the nucleus with the one obtained at the edges of the slit revealed clear differences due…
Photoionization of atomic hydrogen in electric fields: lineshapes
Journal of Physics B, Mar 14, 1994
Fano- and Lorentz-type profile formulae are tested for Stark resonances against exact quantum res... more Fano- and Lorentz-type profile formulae are tested for Stark resonances against exact quantum results. If background terms are included, both work very satisfactorily for a wide range of resonances.
ChemInform Abstract: Transition Metal Complexation (Fischer-Type) of Phosphanylcarbenes
ChemInform, Feb 20, 2001
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Quantum dynamics at conical intersections
Rotation-vibrational states of D2H+ computed using hyperspherical harmonics
Molecular Physics, May 1, 1996
Renner-Teller and spin-orbit interactions between the1A1,1B1and3B1states of CH2
Molecular Physics, Jul 1, 1990
The &(b)tilde;1B1-ã1A1 spectrum of the CH2 radical exhibits singlet-triplet perturbat... more The &(b)tilde;1B1-ã1A1 spectrum of the CH2 radical exhibits singlet-triplet perturbation of the ã and the &(b)tilde; states, even though the direct first-order interaction between the &(b)tilde;1B1 and &(X)tilde;3B1 states is forbidden. We have derived a model for such interactions that involves both Renner-Teller and spin-orbit coupling. The results of calculations made using this model show that the effect of the
High-Resolution Electronic Spectroscopy of Small Molecules
CRC Press eBooks, Aug 2, 2017
Chemical Physics Letters, Feb 1, 2021
263 264 KOTARO OIKAWA such that oo e Γ* is called the outer boundary of D. 3. We call a region D ... more 263 264 KOTARO OIKAWA such that oo e Γ* is called the outer boundary of D. 3. We call a region D a circular (or radial) slit disk if 0 eΰ, D c (\z\ < R <oo), the outer boundary is | 2 |-i?, and every other boundary component is either a point or an arc on | z | = const, (or a line segment on arg z = const.). 2 The stability problem of boundary components* 4. Let Z) be a plane region and let Γ be a boundary component. Sario [16, 17] gave the following classification: (a) If f(Γ) is a point for every univalent function w = f(z) on D, then Γ is said to be weak. (b) If /(Γ) is a continuum, i.e., a connected closed set containing more than one point, for every /, then Γ is said to be strong. (c) If Γ is neither weak nor strong, it is said to be unstable. Weak boundary components were first investigated by Grotzsch in connection with the so-called "Kreisnormierungsproblem" (Grotzsch [7] see also Denneberg [5] and Strebel [21]). He called them vollkommen punktformig. Regions of class O SB = O SD introduced by Ahlfors and Beurling [2] coincide with those possessing merely weak boundary components. Sario [16] has generalized the concept weak boundary components for open Riemann surfaces. It has been discussed also by Savage [19] and Jurchescu [10]. We are now lead to the following natural problems: PROBLEM A. Given a boundary component consisting of a single point, determine whether it is weak or unstable. PROBLEM B. Given a boundary component consisting of a continuum, determine whether it is strong or unstable. We shall attempt to obtain concrete tests with practical applicability. 3. Related extremal problems* 5. Let D be a region containing the point z = 0. Let S3 be the family consisting of all functions w = φ(z) which are regular and univalent in D-{0}, and have the expansion \\z + cz + near z = 0. Consider, with Grotzsch [6], the diameter of the image φ(Γ) of the boundary component Γ. It is quite easy to see that Γ is weak if and only if sup^gςg diam φ(Γ) = 0, and Γ is strong if inf^e^diam φ{Γ) > 0. 6. Let gr be the family consisting of functions w-f(z) such that (i) regular and univalent in D, (ii) /(0) = 0 and/'(0) = l,
Renner Teller and Spin-orbit Perturbations in Triatomic Molecules
Fermi Resonance Perturbations of Orbital Angular Momentum (Renner-Teller) Coupling in Triatomic Molecules: The Stretch-Bender Approach
$^{a}$ Molec. Phys. 40, 1 (1980) $^{b}$ Molec. Phys. 43, 255 (1981) $^{c}$ B. C. Chang, M. Wu, G.... more $^{a}$ Molec. Phys. 40, 1 (1980) $^{b}$ Molec. Phys. 43, 255 (1981) $^{c}$ B. C. Chang, M. Wu, G. E. Hall and T. J. Sears J. Chem. Phys. 101, 9236 (1994)
VizieR Online Data Catalog: ExoMol molecular line lists for H3+ (Mizus+, 2017)
VizieR Online Data Catalog, Mar 1, 2017
Springer eBooks, 1988
The asymptotic solution for a hydrogen atom in a uniform magnetic field of arbitrary strength is ... more The asymptotic solution for a hydrogen atom in a uniform magnetic field of arbitrary strength is obtained. It is derived in the form of common exponential factor multiplied by a finite power of radius time a power series in two variables, the sine of the cone angle and the inverse of radius, with explicit recurrent relations for the coefficients of the power series. It is proven that there exists only one physically acceptable solution in this form. Combining this solution at some radius R with similar series solution in the form of a power series in the radial variable with coefficient being polynomials in the sine, determines the binding energies and wave functions of bound states. To illustrate the usefulness of this approach, the ground-state binding energy of the magnetic field Bϭ100 ͑in units of 2.35ϫ10 9 G) has been computed with accuracy in 10 Ϫ12 hartree. The precision required is Ϸ30 decimal digits, while the previous result of the same accuracy obtained by direct numerical summation of the series using simple exponential decay as the boundary conditions at finite radius R has been computed in high-precision arithmetic of Ϸ280 decimal digits. The accuracy of the binding energies of the excited state evolving from 2s 0 exceeds that of previous calculations.
Three Particle Systems and Hyperspherical Harmonics
The general quantum mechanical description of three particle systems is a challenge, in particula... more The general quantum mechanical description of three particle systems is a challenge, in particular if higher values of the total angular momentum, J, are required and large amplitude internal motions are strongly coupled, being also coupled to the overall rotation. For J = 0 only 3N — 6, here three internal degrees of freedom need to be considered. However, for J ≠ 0, with strong coupling of the internal motions with the overall rotation, it is necessary to consider all 3N — 3, here six degrees of freedom explicitly and simultaneously. Such a fully general quantum mechanical description of three particle systems would be desirable: i. for the bound states of a variety of three particle Coulomb systems, i.e. H-, He, H 2 + etc; ii. for the rotation vibrational states of triatomics, in particular if large amplitude motions are expected with strong Coriolis coupling; and iii. for the characterisation of the reactive scattering of an atom with a diatomic molecule, i.e. the simplest, elementary chemical reaction.
A quantum electrodynamics (QED) correction surface for the simplest polyatomic and polyelectronic... more A quantum electrodynamics (QED) correction surface for the simplest polyatomic and polyelectronic system H + 3 is computed using an approximate procedure. This surface is used to calculate the shifts to vibration-rotation energy levels due to QED; such shifts have a magnitude of up to 0.25 cm −1 for vibrational levels up to 15 000 cm −1 and are expected to have an accuracy of about 0.02 cm −1. Combining the new H + 3 QED correction surface with existing highly accurate Born-Oppenheimer (BO), relativistic and adiabatic components suggests that deviations of the resulting ab initio energy levels from observed ones are largely due to non-adiabatic effects.
The first studies of the 2 A 1-2 B 1 electronic band system of the AsH 2 and AsD 2 radicals were ... more The first studies of the 2 A 1-2 B 1 electronic band system of the AsH 2 and AsD 2 radicals were made at Sheffield University in the period from1966 to 1968 by Dixon, Duxbury and Lamberton using flash photolysis of arsine and deuterated arsine. The bands have a complex rotational structure associated with that of an asymmetric rotor. Band centres of the 0,v 2 ,0-0,0,0 progression were identified for v 2 '=0 tp v 2 '=5, although only the structure of the bands from v 2 '=1 to 3 was analysed in detail. After a long time interval in 1986 a low resolution emission spectrum of AsH 2 was recorded by NI et al. However, it was not until 2007 that He and Clouthier studied the electronic transition of jet-cooled AsH 2 using laser induced fluorescence and wavelength-resolved emission. Following on from this in 2009 Zhao and colleagues recorded absorption spectra of the AsH 2 radical by cavity ringdown spectroscopy. Finally in 2012 Grimminger and Clouthier recorded the equivalent transitions in AsD 2 and AsHD. They also carried out ab initio calculations. By comparing the recent spectroscopic results with those of Dixon et al, we wish to show the complementarity of the different methods for understanding the behaviour of AsH 2 and AsD 2 radicals.
Understanding the adiabatic approximation; the accurate data of H2 transferred to H3(+)
Polish Journal of Chemistry, 1998
Journal of Physics B, Nov 10, 2017
Calculation of the rotation-vibration spectrum of H + 3 , as well as of its deuterated isotopolog... more Calculation of the rotation-vibration spectrum of H + 3 , as well as of its deuterated isotopologues, with near-spectroscopic accuracy requires the development of sophisticated theoretical models, methods, and codes. The present paper reviews the state-of-the-art in these fields. Computation of rovibrational states on a given potential energy surface (PES) has now become standard for triatomic molecules, at least up to intermediate energies, due to developments achieved by the present authors and others. However, highly accurate Born-Oppenheimer (BO) energies leading to highly accurate PESs are not accessible even for this two-electron system using conventional electronic structure procedures (e.g., configuration-interaction or coupled-cluster techniques with extrapolation to the complete (atom-centred Gaussian) basis set limit). For this purpose highly specialized techniques must be used, e.g., those employing explicitly correlated Gaussians and nonlinear parameter optimizations. It has also become evident that a very dense grid of ab initio points is required to obtain reliable representations of the computed points extending from the minimum to the asymptotic limits. Furthermore, adiabatic, relativistic, and quantum electrodynamics (QED) correction terms need to be considered to achieve near-spectroscopic accuracy during calculation of the rotation-vibration spectrum of H + 3. The remaining and most intractable problem is then the treatment of the effects of non-adiabatic coupling on the rovibrational energies, which, in the worst cases, may lead to corrections on the order of several cm −1. A promising way of handling this difficulty is the further development of effective, motion-or even coordinate-dependent, masses and mass surfaces. Finally, the unresolved challenge of how to describe and elucidate the experimental pre-dissociation spectra of H + 3 and its isotopologues is discussed.
Accurate double many-body expansion potential energy surface for triplet H3+. II. The upper adiabatic sheet (2 3A′)
Journal of Chemical Physics, 2004
We report on a global potential energy hypersurface for the upper sheet of the lowest triplet sta... more We report on a global potential energy hypersurface for the upper sheet of the lowest triplet state of H3+. The analytic representation is based on the double many-body expansion theory. The ab initio data points, calculated with a large cc-pV5Z basis, are represented with a root mean square deviation of only 5.54 cm(-1) in the energy region below the H(+)+2H(2S) dissociation threshold. The quasi-bound vibronic states supported by this surface have also been calculated.
Renner-Teller correlation diagrams for orbital angular momentum in Π and Δ states of triatomic molecules
Molecular Physics, Oct 20, 1996
A method is described for relating the energy level correlation diagrams introduced by Renner to ... more A method is described for relating the energy level correlation diagrams introduced by Renner to the angular momentum 'sawtooth' correlation diagrams constructed by Jungen and Merer. In order to do this new spin-orbit coupling versions of the diagrams are introduced for the strictly linear and bent-linear behaviour, and a version of the linear 'sawtooth' diagram is constructed. Finally the effects of vibrational resonances are introduced to modify the interference effects seen in the 'sawtooth' diagrams. The diagrams are constructed using an extension of the calculation method first introduced by Barrow, Dixon and Duxbury to allow to be obtained.
The gas-phase structure of dimethyl peroxide
Physical Chemistry Chemical Physics, 2017
To understand the spectroscopic properties of a molecule that performs large-amplitude motion, di... more To understand the spectroscopic properties of a molecule that performs large-amplitude motion, distinction must be made between the statical and dynamical structures.
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Papers by alexander alijah