Excited-state site effects in luminescence spectroscopy of SH radicals in krypton matrices: Experiment and simulations

The specific features in luminescence spectra of SH radicals in solid krypton differing remarkably from those of SH and OH species in various rare-gas matrices are discussed. Of special interest in Kr matrices are two bands appearing in the SH emission spectra under the $A 2Σ+←X 2Π$ excitation, which center at 375 and 413 nm and possess very different lifetimes, 350 and 750 ns. Along with the experimental findings, we describe the results of the mixed quantum-classical molecular dynamics simulations of the emission spectra performed on the diatomics-in-molecules potential energy surfaces of the ground and excited states of the clusters $SH@Krn$ $(n⩾250).$ The simulations show that both bands in the emission spectra refer to the same $(A 2Σ+,v′=0→X 2Π,v″)$ transition and originate from two different trapping sites in the excited state. The band at the shorter wavelength corresponds to the site with a relatively free movement of SH (A) inside the lattice while the adjacent more intense band at the longer wavelength is associated with the site where one of the matrix atoms is attached to the guest molecule forming a transient complex $SH(A)⋅Kr$ inside the solvation shell.