Ab Initio Intermolecular Potential Surface Research Articles

Semiclassical modeling of infrared pressure-broadened linewidths: A comparative analysis in CO2–Ar at various temperatures

A novel semiclassical approach, which makes use of the exact trajectory implemented within the Robert–Bonamy formalism, is employed for modeling infrared pressure-broadened linewidths. As a prototype, the carbon dioxide molecule perturbed by argon is examined in the temperature range 160–760 K, for which various measurements and computations are available. For a meaningful comparison with previous theoretical works done with both semiclassical and quantum approaches, the ab initio intermolecular potential surface of Parker et al. [J. Chem. Phys. 64, 1668 (1976)] is used. Our values are found to be in agreement with up-to-date experimental data at all temperatures studied.

The dependence of intermolecular interactions upon valence coordinate excitation: The υHF=4 levels of ArHF

The valence state dependence of the Ar–HF interaction potential is extended to υHF=4. Three new ArHF (υHF=4) states, (4000), (4100), and (4110), are observed between 14 780 and 14 880 cm−1 using intracavity laser induced fluorescence. The term values and rotational constants of these states are the following: (4000) ν0=14 783.603 23(30) cm−1, B=0.103 606 8(68) cm−1; (4100) ν0=14 867.419 06(70) cm−1, B=0.102 612(27) cm−1; and (4110) ν0=14 875.048 30(39) cm−1, B=0.103 217(19) cm−1, respectively. The spectral red shifts of ArHF (υ000) dramatically increase from 9.654 cm−1 at υ=1 to 48.024 cm−1 at υ=4. The rotational constant of ArHF(4000) increases essentially linearly with HF valence excitation, becoming 1.3% (40 MHz) greater than that observed at υ=0. At υ=4, the outer classical turning point of HF is extended by 0.4 Å from re, and there is no evidence for Ar–H repulsion. The spectral red shift for linear hydrogen bonded Ar–HF(υ000) indicates a strong enhancement of binding energy upon HF valence bond excitation, while the rotational constant reveals an almost surprising decrease in heavy atom separation. Both the T-shaped ArHF(υ110) and antilinear Ar–FH(υ100), however, show very little dependence of binding energy upon υHF valence excitation. These observations are in good accord with the ab initio intermolecular potential surface.