The isotopic dependence of axes switching in thiophosgene induced by A˜1A2(nπ∗)←X˜1A1 electronic excitation

Abstract: A line-by-line rotational analysis of a selected group of bands in the high-resolution fluorescence excitation spectrum has been carried out to derive the structure of thiophosgene in the à 1 A 2(nπ∗) or S 1 electronic state. The fit of the rotational line structure yields changes of +0.094Å for the CS bond relative to the S 0 value of 1.600 and −0.007Å for the CCl bond (1.727Å). The ClCCl bond angle increases by +6.4° (111.2°) while the out-of-plane angle advances to 23.9°. The in-plane a- and b-principal axes are susceptible to axis-switching mediated by chlorine 35–37 isotope substitution and also by excitation to the à state. In the or S 0 ground state, the a-axis lies along the CS bond for the 35Cl2CS isotopomer and switches under chlorine isotope substitution in 37Cl2CS to the in-plane perpendicular direction. Electronic excitation also induces a/b axis-switching giving rise to anomalous rotational line intensities in the centers of the 35Cl2CS bands. [Copyright &y& Elsevier]