Phosphorescent Decay Time of Matrix-Isolated GeO, GeS, SnO, and SnS, and the Lifetime of the Cameron Bands of CO-Type Diatomics

The lifetime for the Cameron bands, $a^3{\mathrm{\Pi \hspace{0.17em}\to \hspace{0.17em}X}}^1\Sigma$ , of GeO, GeS, SnO, and SnS has been measured in argon, krypton, and xenon at 20 and 33°K, and in SF₆ at 20, 33, and 77°K. The values range from 100 μsec to 3 msec, depending on molecule, matrix, and temperature. The external heavy atom effect on lifetime is strongest for light solutes. The internal heavy atom effect, expressed as the ratio of lifetimes, is in excellent agreement with predictions by first‐order perturbation theory. Therefore, we used this theory to estimate the lifetime of the Cameron bands of CO, CS, SiO, and SiS in argon. The matrix observations are then used to deduce values for the lower limit of the corresponding gas‐phase lifetimes. It is demonstrated that, for forbidden transitions, lifetimes of matrix‐isolated molecules are a useful tool to estimate unknown gas‐phase values.