Knowledge Bank

The absorption, laser excitation, and resolved fluorescence spectra of 9-Hydroxyphenalenone and of its methyl-substituted derivatives in solid neon are reported. Analysis of the spectra yields detailed information about the potential function and proton tunnelling both in the $S0$ ground state and in the $S1$ excited state. Studies of vibrationally unrelaxed fluorescence yield new insights into the rates and mechanisms of vibrational relaxation and energy redistribution. The methyl substitution is found to increase the relaxation rates by at least an order of magnitude. This is interpreted by the presence of a nearly freely rotating $CH3$ group and attributed to a $V\to R$ type process.