Studies on the Intermolecular Potential and its Anisotropy.
Abstract
Nuclear spin-lattice relaxation times (T _1) have been measured for ^ {19}F in the SeF_6 and TeF_6 molecules. These measurements have been made in the pure gases SeF_6 and TeF_6 and with each of these pure gases in various buffer gases. Buffer gases include Xe, Kr, Ar, CH_4, CF_4 , N_2, CO, CO_2 , HCl, SF_6, and O _2. It has been found that except for SeF _6 in O_2 and TeF_6 in O_2 , all of the probe-buffer systems (probe = SeF _6 or TeF_6) studied relax via the spin rotation relaxation mechanism. Relaxation times were measured as a function of temperature and density. In the case of oxygen gas as a buffer, there were two dominant mechanisms for spin relaxation: spin rotation (intramolecular) and nuclear spin electron spin dipole-dipole interaction (intermolecular). The semiclassical and classical theories of nuclear spin relaxation by Gordon related these results to cross sections for the transfer of rotational angular momentum. These cross sections include both changes in molecular reorientation as well as the effects of rotational inelasticity (changes in the magnitude of the J vector) and have been determined for all of the collision pairs mentioned above. The intermolecular interactions which cause these changes in the rotational angular momentum are due to the anisotropy of intermolecular forces which depend on the relative orientation of the colliding pair. Collision efficiencies obtained from these cross sections increase with increasing polarizability of the buffer gas, indicating sensitivity to dispersion forces. The temperature dependence of the relaxation times (T_1) have been determined by this study and hence, the temperature dependence of the cross sections for each collision pair. The cross sections obtained from the spin relaxation studies are given as experimental data which may be used with other observables to construct potential energy surfaces for the collisional pairs studied.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1989
- Bibcode:
- 1989PhDT........43T
- Keywords:
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- Chemistry: Physical; Physics: Molecular; Physics: Atomic