The molecular structure of hydrogen disulfide (H2S2) and barriers to internal rotation

Abstract

The molecular structure of H/sub 2/S/sub 2/ has been determined by ab initio molecular theory at the SCF and CI-SD levels. The SCF and CI-SD results are in good agreement with each other for all parameters and are in agreement with experiment except for the value of theta(HSS). The calculated value for theta is 98.4/sup 0/ as compared to an experimental value of 91.3/sup 0/. It is suggested that the experimental value is too low. The vibrational frequencies for the optimum skew structure and the cis (tau = 0/sup 0/) and trans (tau = 180/sup 0/) structures have been calculated at the SCF level. The cis and trans structures have one imaginary frequency and are true transition states on the internal rotation energy surface. The barriers to internal rotation were calculated at the SCF and CI-SD levels and were corrected for the difference in zero-point energies; this correction is 0.6-0.7 kcal/mol. The trans barrier is 5.0 +/- 0.15 kcal/mol and the cis barrier is 7.5 +/- 0.15 kcal/mol. 22 references, 3 tables.