Min-Chieh Yang

Electronic spectroscopy and excited state dynamics of the Ar⋅SH complex

The laser excitation spectrum A (0,00,vS’)−X (0,00,0), has been observed for the Ar⋅SH complex. Rotational constants and bond lengths have been obtained for vibrational levels of the A and X states. A remarkable lengthening of the A state natural lifetime is observed upon Ar complexation.

Electronic spectroscopy of the R⋅SH (R=Ne, Ar, Kr) complexes

The laser induced fluorescence spectra of the thiohydroxyl radical inert gas complexes, R⋅SH (R=Ne, Ar, and Kr) are reported. The spectra of numerous isotopomers involving 32S, 34S, 84Kr, 86Kr, 1H, and 2H have been observed. By using isotopic shifts of the heavy atoms, and other observations, the overwhelming majority of the 60 observed vibronic transitions have been assigned as originating from the vibrationless level of the X 2Π state and terminating on specific vibrational levels (vSH, vbk, vs) of the A 2Σ+ state, where nominally vs is the R-SH stretch, vSH is the SH monomer stretch, and vbk is the bending vibration. Vibrational frequencies, ωe, and anharmonicities, ωexe, for many of the modes are obtained, as well as dissociation energies (assuming a simple model) for both the A and X states of the R⋅SH complexes.

Characterization of the ground X̃ 2Π state of the complexes R⋅SH (R=Ne,Ar,Kr)

Information characterizing the X  2Π state of the R⋅SH (R=Ne,Ar,Kr) complexes has been obtained from two complementary experimental techniques. The spin-vibronic energy levels have been determined by wavelength resolved fluorescence spectroscopy subsequent to laser excitation of specific vibrational levels of the A 2Σ+ state. In addition, several “hot” bands from excited spin-vibronic levels of X 2Π Ne⋅SH have been observed and assigned. The experimental data have been used to construct a simple model for the ground state potential energy surface for each complex. These models show that the most stable conformation for each complex is linear H-bonded, but the barrier to isomerization to the S-bonded complex is quite low. The overall bonding is somewhat weaker and more isotropic than the corresponding hydroxyl complexes.

Jahn—Teller coupling in the [Xtilde] 2E ground states of the CF3O and CF3S radicals

The Jahn—Teller and spin—orbit coupling in the ground states of the CF3O and CF3S radicals have been investigated experimentally by dispersed fluorescence spectroscopy. These spectra are analysed using a theoretical model that simultaneously includes spin—orbit coupling and multimode Jahn—Teller coupling, both linear and quadratic. We find that in each of these radicals a moderate linear Jahn—Teller effect exists in ν6, with a much smaller coupling in ν5. These results are compared and contrasted with those for the related radicals CH3O and CH3S. The experimental data and theoretical analyses of these four radicals represent the most thorough investigations to date of the combined effects of spin—orbit and Jahn—Teller coupling.

Competition between radiation and photofragmentation in the à 2Σ+ state of the SH/D rare gas complexes

The natural lifetimes of a large number of the vibrational levels of the excited A 2Σ+ electronic state of the family of rare gas complexes, R⋅SH (R=Ne, Ar, and Kr) and their deuterides, are reported. It is well known that the natural lifetime of the A 2Σ+ state of isolated SH/D is markedly shortened by a photofragmentation process. Our results for the complexes show that the rare gas atom plays an important role in inhibiting this process. From a classical model of the molecular system we are able to explain the trends observed in our lifetime data. The data from the R⋅SD complexes where for some vibrational levels the deuterium atom appears to be trapped between the rare gas and sulfur atoms allows us to establish a radiative lifetime for these complexes and the SH/D monomer.