Quasidegenerate Levels Research Articles

Vibrational energy transfers in polyatomic molecules: a vibrational effective Hamiltonian approach for the CO 2-Ar system

This paper represents the first attempt at applying the quasi-degenerate perturbation theory to the problem of vibrational relaxation in an atom + polyatomic molecule system. The theory is illustrated by the CO 2 + Ar collision study. The vibrational spectrum of the isolated CO 2 molecule is partitioned into several groups of quasi-degenerate levels. Then the vibrational part of the CO 2 + Ar Hamiltonian depending on the two parameters R (distance between the two centers of mass) and γ (angle between the R and the OO axis) is block-diagonalized using a new wave operator for mulation. This scheme is reproduced at the nodes of a ( R, γ) grid and the results, i.e. the eigenvalues and the non-adiabatic couplings, are interpolated in this two-dimensional space using third-order spline functions. A simple qualitative analysis of these curves provides an appreciation of the relative weight of various relaxation paths starting from the initial states (010) and (001).

Treatment of long-range couplings in collisional charge transfer from H(1s) to fully-stripped ions

Electron transfer from H(1s) to a fully-stripped ion of charge + Z A occurs dominantly to excited levels ( n⪅ Z A), for low to intermediate collision energies ( E⪅20 keV/amu). To compute cross sections for capture into individual states (e.g., for predicting radiative emission in a plasma) it is necessary not only to solve the molecular-state close-coupling problem entailed in the primary charge-transfer event, but also to treat the effects of long-range dipole and quadrupole couplings produced by the receding proton among the n 2 quasi-degenerate levels with a given principal quantum number n. A simple, computationally efficient solution to the long-range coupling problem can be given, based on an application of the exact solution for the dipole coupling problem given previously by Demkov et al. (1974) [10,11]. If the quadrupole couplings are treated by the first Magnus approximation, the entire long-range coupling problem is reduced to calculation of the n × n matrix representation of a finite rotation for angular momentum j= 1 2 (n−1) , and the evaluation of simple numerical quadratures.

New measurements and improved calculations of self-broadening coefficients of lines in the v 2 band of H 216O

From Fourier transform spectra (resolution ≈ 0.005 cm -1), the self-broadening coefficients of 16 doublet-lines, involving quasi-degenerate levels of the (000) and (010) vibrational states of water, have been measured using methods previously described. For doublet-lines, it is observed that self-broadening is about 40% smaller than for other lines. This effect is well reproduced by a calculation based on the Anderson-Tsao-Curnutte method, if one takes into account the four following intermolecular interactions: dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole. This improved calculation is also used to recalculate our set of 150 previously reported self-broadening coefficients: on the whole, the agreement between measured and calculated values is improved by about 18% as compared to the calculated values of Benedict and Kaplan instead of 14% for our previous calculations based only on the dipole-dipole intermolecular interaction. It is also demonstrated that the influence of the quadrupole moment is larger for doublet-lines than for other lines. Finally, the Anderson-Tsao-Curnutte method, taking into account the four intermolecular interactions mentioned above, leads to relative differences between observed and calculated values less than 20%, for 72% of the 166 measured lines.