Journal of Physical Chemistry B, Vol.107, No.36, 9711-9716, 2003
Electronic spectra of SCnH radicals (n=2-4): An ab initio study
The MCSCF and MRCI methods have been used to study the electronic spectra of SCnH radicals for n = 2-4. Vertical excitation energies and oscillator strengths have been computed for a number of states. The lowest-lying excited doublet states are due to an excitation from the highest inner-valence T orbital to the HOMO, which is of T type. The corresponding vertical excitation energies are compared to the experimental results. We encountered very intense transitions to high-lying (2)Pi terms [4(2)Pi <-- X-2Pi (n = 2), (6,7)(2)Pi <-- X(2)Pi (n = 3), and (7,8,9)(2)Pi <-- X(2)Pi (n = 4)], as well as moderately intense transitions to lower-lying terms [1(2)Pi <-- X(2)Pi, 1(2)Sigma(+) <-- X(2)Pi (n = 2), (2,3,4)(2)Pi - X(2)Pi(n = 3), and 1(2)Pi - X(2)Pi (n = 4)]. These intense transitions are frequent in cumulenic carbon chains but have not been registered so far in the present systems. The X(2)Pi - 1(4)Pi vertical energy gaps are (in electronvolts) 4.94 (n = 2), 2.87 (n = 3), and 3.71 (n = 4); the adiabatic electronic energy gaps should be about 1.95, 0.42, and 0.93 eV smaller, respectively.