Vibrational dynamics of SCCl2 from the zero point to the first dissociation limit

Abstract

Over one thousand ← vibronic transitions of the SC³⁵Cl₂ and SC³⁵Cl³⁷Cl isotopomers, originating from eight state vibrational levels, have been measured by dispersed fluorescence spectroscopy and stimulated emission pumping. The observed ground state vibrational energy levels involve all six vibrational modes, and have up to 28 quanta of combined excitation. The energy window extends from the fundamental vibrations to beyond the molecular dissociation limit near E/h = 600 THz. 375 ground state vibrational levels of SC³⁵Cl₂ have been assigned and fitted to an effective Hamiltonian. 35–37 chlorine isotopomer splittings are regular except for a few resonances when v₁ ≥ 7 and v₄ ≥ 6. Regular progressions up to 600 THz indicate the conservation of at least two good vibrational quantum numbers at the SCCl–Cl and SC–Cl₂ dissociation limits. A subset of over 100 transitions up to E/h = 240 THz was used to refine a 6-D ab initio potential surface represented in bond distance coordinates. This surface, together with a previously computed state potential surface and transition dipole surface, also reproduces the spectral intensities of the ν₁–ν₄ polyads up to E/h = 240 THz. SCCl₂ is an excellent model system for intramolecular vibrational redistribution (IVR) among skeletal vibrations ranging from isolated resonances to extensively mixed quantum states. The newly extended spectra show that half of the 6-D quantum state space remains highly structured up to the first dissociation limit near 600 THz, resulting in sub-exponential IVR dynamics except at short times.