Thioformaldehyde single rotational level photophysics: Longer than radiative lifetimes and reduced fluorescence yields in the isolated molecule

Abstract

Fluorescence lifetimes and Zeeman quantum beats of single rotational levels in 3 B 2 carbon disulfideFluorescence polarization as a probe of the rotational dynamics of isolated highly excited molecules J. Chem. Phys. 81, 629 (1984); 10.1063/1.447744Single rotational level fluorescence quantum yields, radiative lifetimes, and nonradiative decay rates of S 1 D2CO and H2CO(A1 A 2, 41): Rotational dependence Single rotational level fluorescence lifetimes and relative fluorescence quantum yields have been measured under collision-free conditions for a variety of rotational levels in the 4 1 vibrational state of SI H2 CS. About half of the rotational levels studied decay with a radiative lifetime of ::::: 170 j.lS. Other levels decay with lifetimes longer than the radiative lifetime and these states correlate with perturbations observed in the spectrum, as detected by Dopplerlimited laser-induced fluorescence and sub-Doppler intermodulated fluorescence techniques. The levels coupled to TI and most of the levels coupled to So have relative fluorescence yields near unity. A few levels in SI show reduced quantum yields of fluorescence which persist at pressures as low as 5 X 10 -7 Torr. A sequential coupling model is proposed to qualitatively account for the observed excited state dynamics of these levels.

The Mechanism of Magnetically Tuned Singlet–Triplet Avoided Crossings in the Ã1A2–X̃1A1 410 Band of Thioformaldehyde H2CS

“…Ã 1 A 2 singlet levels have also been found to be weakly perturbed by highly excited rovibrational states (X*) of the ground state using sub-Doppler techniques (6). An extensive search for zero-field perturbations especially in the 4 1 Ã 1 A 2 vibronic manifold has been carried out by lifetime measurements (7) and by subDoppler intracavity spectroscopy combined with a statistical analysis (8).…”

“…a T 0 is the band origin, the other parameters have been defined in Eqs. [3], [6], and [7]- [11]. 193…”

Toward a Unified Analytical Description of Internal Conversion and Intersystem Crossing in the Photodissociation of Thioformaldehyde. I. Diabatic Singlet States

“…Thioformaldehyde has been the subject of both experimental and theoretical photochemical studies. Most experimental studies explored the ro-vibronic states obtaining energy levels, fluorescence, and phosphorescence lifetimes. − The singlet–triplet interactions have been identified as perturbations. , Very few experimental studies have paid attention to the dynamic mechanism of photodissociation of thioformaldehyde. On the other hand, previous ab initio calculations of thioformaldehyde mainly focus on the electronic absorption spectrum, ranging from valence excited states to Rydberg excited states. − Only a few have explored the reaction mechanism of photodissociation by identifying critical points and approximate reaction paths. − …”

Observation of vibronically excited thioformaldehyde at 62,000–72,000cm−1 by 1+1′+1′ resonance enhanced multiphoton ionization spectroscopy

“…Thioformadehyde (H 2 CS), unstable as a monomeric species under normal conditions, is the simplest molecule in the thiocarbonyl family [1]. It is also an important intermediate in organic synthesis [2,3], biological functions [4][5][6], photochemical reactions [7][8][9][10], and astronomical systems [11,12]. In early spectroscopic studies, the ionization energy (IE) and heat of formation of H 2 CS were determined by Lossing and Jones using electron impact mass spectroscopy [7].…”