Experimental and theoretical study of rotationally inelastic polar molecule collisions: /sup 7/LiH--HCN

Journal Article · Sun Jun 15 04:00:00 EDT 1980 · J. Chem. Phys.; (United States)

OSTI ID:5428761

Dagdigian, P J; Alexander, M H

This article describes the study of rotational energy transfer in the strongly polar LiH--HCN system. A supersonic beam of LiH, rotationally state selected in j/sub a/=1 by an electric quadrupole field, is scattered by HCN gas at room temperature. Laser fluorescence detection is used to determine integral cross sections for j/sub a/=1..-->..j'/sub a/ LiH transitions. The measured cross sections (in A/sup 2/) are 245 +- 30 (2sigma), 519 +- 88, 222 +- 47, 125 +- 26, 64 +- 17, and 41 +- 12 for j'=0,2,3,4,5, and 6, respectively. The large magnitudes of the cross sections reflect the strong, long-range dipolar coupling. A comparison is made with the predictions of various theoretical models, based on the approximate solution of the time-dependent classical-path equations of motion for rectilinear trajectories. The usual Born approximation significantly overestimates the cross sections for the dipole allowed (j/sub a/..-->..j/sub a/ +- 1) transitions, even when statistical microreversibility is imposed. Worse, extension of the Born approximation to second order appears to introduce even larger errors. Better agreement with experiment is obtained within the sudden approximation, although the predicted j/sub a/=1..-->..j'/sub a/=0,2 cross sections are still too large, due to the breakdown of this approximation at large impact parameter for this long-range system. This can be remedied in the adiabatically corrected sudden (ACS) approximation, which we have recently developed, by the introduction of an effective dephasing frequency into the sudden action integral. In a confirmation of our earlier study of the LiH--HCl, DCl systems, we find that the ACS cross sections are in good agreement with the experimental values, especially for the strongest transitions.

• Research Organization: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
• OSTI ID: 5428761
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 72:12; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ALKALI METAL COMPOUNDS
COLLISIONS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HYDRIDES
HYDROCYANIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
LITHIUM COMPOUNDS
LITHIUM HYDRIDES
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
ROTATIONAL STATES