D.J. Clouthier

Sequential two‐photon absorption and singlet–singlet energy pooling in thiophosgene vapor

Emission from the second excited singlet state of Cl2CS vapor has been monitored following excitation with a tightly focused, pulsed dye laser in the region of the ground state to first excited singlet and triplet absorption systems. Excitation in the triplet bands produces prompt fluorescence from S2 as a result of sequential two‐photon absorption, S0→hνT1→hνS2. Excitation in the bulk of the singlet bands produces no prompt fluorescence but does produce delayed fluorescence as a result of a bimolecular singlet–singlet energy pooling process, 2S1→S2+S0.

Structures and decay dynamics of thiocarbonyl excited states

Abstract Gas phase absorption, emission and emission excitation spectra have provided detailed ground and excited state structural information for several representative small thiocarbonyls. The ground states are planar but the excited states are generally non-planar and may exhibit a large variation in inversion barrier heights and equilibrium out-of-plane angles. The CS bond is elongated in excited states, by as much as 0.5 A in the S 2 1 (π,π*) states of Cl 2 CS and ClFCS. Tetra-atomic thiocarbonyls appear to decay solely by radiative means from bound levels of their S 1 1 (n,π*) states under collision-free conditions; radiative decay of the corresponding T 1 states has not been observed. Excitation to low-lying vibrational levels of the S 2 states of ClFCS and Cl 2 CS in the gas phase results in S 2 → S 0 emission with high quantum yields (ϕ f → 1.0). At higher vibrational energies non-radiative decay (probably leading to dissociation) dominates. The observation of intense emission from S 2 has been exploited to probe the mechanisms of the two-photon absorption in gas phase Cl 2 CS. Sequential two-photon absorption via T 1 and bimolecular singlet—singlet energy pooling have been observed.

Photophysics of the B̃ 1A1 state of thiophosgene

Abstract The results of fluorescence lifetime measurements using a dye laser excitation source are combined with other recently published data to present a consistent picture of the photophysics of the B 1 A 1 state of Cl 2 CS.

Second excited singlet state emission spectroscopy of thiocarbonyls. I. Thiophosgene

Abstract Well resolved emission spectra have been recorded after dye laser excitation of low-lying vibronic levels in the B ( 1 A 1 ) state of Cl 2 CS. The effects of substrate pressure, added SF 6 and excitation wavelength on the spectra are reported. A Franck-Condon analysis suggests that the excited state CS bond length is 0.5 A longer than in the ground state.

Second excited singlet state emission spectroscopy of thiocarbonyls. II. Thiocarbonyl chlorofluoride

Abstract Single vibronic level emission spectra have been measured for four excitation wavelengths pumping the second excited singlet state of CIFCS. Only resonance fluorescence is observed. Progressions involving Δv″1 = 0, 1, 2, …, Δv″6 = 0, 2, 4 … dominate. Analysis of the spectra indicates that neither intra- or intermolecular processes lead to odd Δv′6 changes and that collisions in the pure gas lead to electronic quenching of molecules in the excited state.

Laser excitation study of the second excited singlet state photophysics of ClFCS

A tunable dye laser has been used to excite selected single vibronic levels of the ? (1A′) state of ClFCS in the gas phase. Fluorescence (?→?) excitation spectra, quantum yields, and excited state lifetimes have been measured. Radiative and nonradiative decay constants and bimolecular self‐quenching constants have been calculated for each selected state. A model in which a single dissociative vibrational mode provides the sole nonradiative decay mechanism is proposed.

The B̃(1A′) ← X̃(1A′) spectrum of ClFCS

Abstract The vibrational structure of the first strong electronic transition, B 1 A′ ← X 1 A′ , of CIFCS has been analyzed. Four excited state frequencies have been identified. The excited state is nonplanar and has a barrier to inversion of ⪸2000 cm−1 and a CS bond which is about 0.5 A longer than the ground state.