Method of describing highly excited vibrational-rotational states of diatomic molecules

Institute of Applied Physics, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 3, pp. 281–289, March, 1990.     

Highly excited rovibrational states of HNC

The emission spectrum of HCN has been recorded at 1463 K using hot gas molecular emission (HOTGAME) spectroscopy in the wavenumber region of 2900–3500 cm⁻¹ with a resolution of 0.01 cm⁻¹. The dense emission spectrum was analyzed with the spectrum analysis software SyMath™ implemented in the Mathematica™ computer algebra system. This work reports the analysis of the band series up to v₂ = 8 and of the band series up to v₂ = 6.36 rovibronic (v₁, v₂, l, e/f, v₃) substates of HCN including all l = 0, 2, 4, 6, 8 sublevels of the highly excited bending combination mode have been characterized for the first time and for the 22 known vibrational sublevels it was possible to improve the existing spectroscopic constants substantially. 18 (v₁, v₂, l, v₃) vibrational sublevels are located for the first time relative to the 00⁰0 state. The analysis reported here includes rovibrational states up to very large rotational excitations of J = 60–80. For the combination states the rotational states have been determined up to J = 86 which corresponds to 7000 cm⁻¹ rotational excitation energy, this state is only 2000 cm⁻¹ below the isomerization barrier. It was possible to determine for the first time the L_v high order rotational constant for many states reported in this work.     

双原子分子激发态转动传能量子干涉效应模型

物质波的干涉是由于微观粒子具有波的特性而产生的干涉现象.对于双原子分子单三重混合态转动传能过程具有波动特性,两个通道间存在量子干涉效应.基于玻恩近似的微扰理论,本文利用各向异性相互作用势和直线轨迹近似给出了包含干涉相位角的干涉表达式,建立了新的量子干涉模型,并讨论了此模型中利用的近似理论.     

双原子分子激发态转动传能量子干涉效应模型

物质波的干涉是由于微观粒子具有波的特性而产生的干涉现象。对于双原子分子单三重混合态转动传能过程具有波动特性,两个通道间存在量子干涉效应。基于玻恩近似的微扰理论,本文利用各向异性相互作用势和直线轨迹近似给出了包含干涉相位角的干涉表达式,建立了新的量子干涉模型,并讨论了此模型中利用的近似理论。     

On the determination of small electric dipole moments of excited electronic states in diatomic molecules

A new method is proposed for the determination of small electric-dipole moments in diatomic molecules by measuring the induced transitions due to crossed electric and magnetic fields. A theoretical treatment is given for states belonging to Hund's cases (a) and (b), and for states in the intermediate coupling case between Hund's cases (a) and (b). The method is restricted to non-Σ states.     

Electron impact ionization of diatomic molecules

Cross sections for the ionization of N₂, CO and O₂ diatomic molecules by electron impact are calculated. The applied distorted wave model is based on our previous studies for positron impact, the molecular orbitals being described by Gaussian wavefunctions. Our study emphasizes the importance of electron exchange and of using correct distorted waves for the ejected electron.     

Electron spectroscopy using excited atoms and photons: II. Penning ionization of diatomic molecules

A high resolution electrostatic electron analyser has been used to study Penning ionization electron spectra of H₂, HD, D₂, N₂, CO, NO and O₂ using helium metastable atoms (2¹S, 2³S). Results for H₂, N₂ and CO are in good agreement with other work. New data are presented for HD, D₂, NO and O₂. The Penning electron spectra are also compared to the 584 Å photoelectron spectra obtained in the same apparatus. The relative vibrational intensifies for the given electronic bands indicate that in most cases Franck—Condon factors for Penning ionization and photoionization are very similar. However for the O₂⁺(X²Π_g) band, the (2³S) Penning electron and photoelectron spectra show significant differences in the Franck—Condon envelopes This perturbation of the envelope for the Penning ionization may be explained by a competing autoionization process. The relative electronic transition probabilities are in many cases found to be different for Penning ionization and photoionization.     

Nonadiabatic effects in diatomic molecules on resonant continuum Raman scattering

Journal of Applied Spectroscopy -     

Calculations of diatomic molecules with the LCTCO method. Doubly excited states of the H2 molecule

Nonempirical calculations of 20 autoionizing states of the H₂ molecule are performed in a two-center orbital basis and for two values of the internuclear distance. Results obtained are compared with other results known from the literature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 31–34, July, 1986.     

An angular singularity-free method for the dynamics of the rovibrational motion of diatomic molecules

An angular singularity-free method for the dynamics of the rovibrational motion of diatomic molecules has been proposed. The present method is based on a formulation that the orientation of a diatomic molecule is expressed by the Cartesian coordinates of the unit vector parallel to the molecular axis. In this light, the present method can be considered as a modification of a method proposed for the rigid rotational motion to the rovibrational motion. Illustrations of the present method have been performed for the classical dynamics of the rovibrational motion of a diatomic molecule, and for the semiclassical dynamics of the collision between an atom and a diatomic molecule, including comparisons with other conventional methods. It is concluded that the present method is free from angular singularity, and that the present method is superior to other conventional methods in view of computational efficiency.     

Molecular properties of selected diatomic molecules of astrophysical interest

Molecular properties such as bond length, dipole moment, harmonic frequency, IR intensity, atomization energy, electron affinity and ionization potential of the selected diatomic molecules of astrophysical interest have been studied using hybrid density functional HF/DF B3LYP method. The consistency and convergence of the results have been tested with four basis sets from 6-311 + + G (2df, 2pd) to aug-cc-pVTZ with improved size and quality. Most of the results for dipole moment, harmonic frequency, IR intensity, electron affinity and ionization potential are new. The reported results agree well with theoretical and experimental data wherever available.Received: 28 March 2003, Published online: 12 August 2003PACS: 31.15.Ew Density-functional theory - 33.15.Ry Ionization potentials, electron affinities, molecular core binding energy - 33.15.Dj Interatomic distances and angles - 33.15.Fm Bond strengths, dissociation energies     

Electron scattering by polar molecules

Theoretical and experimental studies of electron-polar molecule collisions are reviewed. Principal emphasis is placed on elastic scattering and excitation of rotational states by low-energy (less than about 10 eV) electrons. After a survey of experimental techniques and methods of cross-section calculation, the results are compared with each other. In particular, the dipole-moment dependence of the cross-section is discussed in relation to possible bound states in a dipole field. Examples of applications of the resulting cross-section are demonstrated. Finally future problems are summarized.     

First-principles calculation of excited states of diatomic molecules: a benchmark for the Gutzwiller conjugate gradient minimisation method

We recently proposed the Gutzwiller conjugate gradient minimisation (GCGM) method for efficient and accurate calculation of the ground state total energy of molecular and bulk systems. The GCGM method is developed under the framework of Gutzwiller wave function but goes beyond the commonly adopted Gutzwiller approximation to improve the accuracy and flexibility in treating the correlation effects. In this conference proceeding, we benchmark the GCGM method with the calculation of excited state potential energy curves of three diatomic molecules, namely H₂, N₂, and O₂. Our calculations demonstrate the flexibility and reasonable accuracy of the method.     

Absence of bound states in extremely asymmetric positive diatomic molecules

It is shown that the Hamiltonian for a diatomic molecule consisting ofN electrons and two dynamic nuclei with chargesZ ₁ andZ ₂ has no bound states if one of the charges is sufficiently large. The nuclear motion is completely unrestricted, and the kinetic energy of both nuclei can be included in the Hamiltonian. One of the nuclear charges can be arbitrarily small, provided that the other is sufficiently large.Research supported in part by NSF grant DMS-8908125     

Spin-orbit and spin-rotation coupling in doublet states of diatomic molecules

The spin-rotation interaction and the centrifugal correction to the spin-orbit coupling make indistinguishable contributions to the energy levels of a diatomic molecule in a multiplet state with Λ ≠ 0. A previous method of separating these two contributions, based on the use of the vibrational dependence of the spin-orbit coupling constant, is unreliable. It is suggested here that a better procedure is one based on the isotope dependences of the spin-rotation coupling constant γ and the centrifugal correction to the spin-orbit coupling constant A_D. Both γ_e and A_De are shown to be inversely proportional to μ, the reduced mass of the molecule, but their contributions to the energy have different isotope effects. The method is used to determine values of γ_e and A_De for the X²Π state of HCl⁺, and the form of the spin-orbit coupling function A(r) in the vicinity of the equilibrium bond length is derived. The implications for RKR calculations are considered briefly.     

On Λ-type doubling in multiplet states of diatomic molecules

Explicit expressions valid in the neighborhood of Hund's case (a) and (b) are obtained for the width of Λ-type doubling of multiplet Π terms up to septet multiplicity. Moreover, a relation between the constants occurring in the expressions of Hund's cases (a) and (b) is given.