R.H. Judge

An analysis of the methyl rotation dynamics in the S0 (X̃ 1A1) and T1 (ã 3A2) states of thioacetone, (CH3)2CS and (CD3)2CS from pyrolysis jet spectra

Jet‐cooled, laser‐induced phosphorescence excitation spectra (LIP) of thioacetone (CH3)2CS/(CD3)2CS have been recorded over the region 16 800–18 500 cm−1 using the pyrolysis jet spectroscopic technique. The responsible electronic transition, T1←S0, a 3A‘←X 1A1, results from an n→π* electron promotion and gives rise to a pattern of vibronic bands that were attributed to activity of the methyl torsion and the sulphur out‐of‐plane wagging modes. The intensities of the torsional and wagging progressions in the excitation spectra were interpreted in terms of a C2v–Cs molecular distortion of the triplet molecule from its singlet ground state equilibrium structure. A complete unrestricted Hartree–Fock (UHF) ab initio molecular orbital (MO) structural optimization of the T1 state predicted that the sulphur was displaced by 27.36° from the molecular plane and the methyl groups were rotated by 10.93° in clockwise–counterclockwise directions. Restricted Hartree–Fock (RHF) calculations were used to generate the V(θ...

The far ultraviolet spectrum of thioformaldehyde

Abstract The electronic absorption spectrum of thioformaldehyde has been recorded from 2200 to 1800 A. Four electronic transitions have been identified in the spectrum and have been assigned to the π → π*, n → 4s, n → 4p y and n → 4p z electron promotions.

Thioketone spectroscopy: An analysis of the lower electronic transitions in thioacetone and thioacetaldehyde

Abstract Visible and ultraviolet spectra of the unstable species, thioacetaldehyde, CH 3 CHS, thioacetone, (CH 3 ) 2 CS, and thioacetone- d 6 have been studied in the gas phase. The valence n → π* excitations, A ← X and a ← X, have been identified. Rydberg n → 4s, 4p y and 4p z and π → π* valence excitations have been found in thioacetone. In thioacetaldehyde a Rydberg-valence interaction mixes the n ,4s and π,π* states which leads to a broad absorption of mixed character between 200 and 220 nm.

A vibronic analysis of the B̃1A1(ππ∗) ← X̃1A1 electronic transition in thiophosgene

The ultraviolet absorption spectrum assigned to the B1A1(ππ∗) ← X1A1 electronic transition has been photographed under conditions of moderately high resolution. The spectrum proved to be very complicated and only 30% of the observed bands could be assigned. Three progressions were located in the spectrum and were assigned to ν″4, ν′4, and ν′1. Inversion doubling splittings were obtained for a number of cold bands from an analysis of the hot bands in ν″4. The inversion doubling splittings were sensitive to ν1 and ν4. An estimate was made for the barrier to inversion along each of these directions.

Laser excitation spectrum and the long path length absorption spectrum of formyl cyanide, CHOCN

Abstract Formyl cyanide has been prepared for the first time by the flash pyrolysis of methoxyacetonitrile. The compound was found to be unstable and had a half-life of about 8 min in the vapor phase in the laser experiments. The near-UV absorption spectrum was photographed under conditions of long path length (56 m) at modest dispersion (1.5 nm/mm between 368 and 390 nm, and 0.75 nm/mm between 368 and 350 nm). Excitation spectra were recorded over the 386- to 360-nm region with a N2 pumped dye laser. The observed spectrum proved to have an open vibrational and rotational fine structure and was assigned to the n → π ∗ A 1 A″ ← X 1 A′ electronic transition. Vibrational assignments were made in terms of ν′3 (CO), ν′4 (CHO), ν′5 (CC), ν′6 (CCO), ν′7 (CCN), ν′8 (H wag), ν′9 (CCN), ν″7 (CCN), and ν″9 (CCN). The vibrational frequencies in both states were found to correlate closely to those of the propynal molecule.

Thiocarbonyl spectroscopy: Methyl torsional vibrations and internal rotational barriers of thioacetaldehyde in its ã 3A‘ and X̃ 1A’ states

Thioacetaldehyde was prepared by the vacuum flash pyrolysis of 1, 3, 5‐trimethyl‐s‐trithiane and was observed spectroscopically in a rapidly flowing system. The 614 nm absorption system of CH3CHS/CH3CDS/CD3CHS/CD3CDS was recorded photographically at path lengths of 72 m. Phosophorescence excitation and emission spectra of CH3CHS were observed with a cw dye laser. The assignment of the first absorption system was made to the spin forbidden transition a 3A‘←X 1A’. The bands observed in the region of the origin proved to have a very complex structure, and were assigned to torsional transitions. The observation of several hot band progressions which could be fitted to levels derived from microwave data gave the parameters V‘3 =534.3 cm−1, F‘=6.9950 cm−1, and ν0=16 293.8 cm−1 for CH3CHS. The fit to the excited state torsional levels was less satisfactory and gave V3 =94.18 cm−1, F’=5.3608 cm−1. An analysis of the data for the other isotopic species showed that the torsional motion in the upper state was coup...

The Ã1A″ ← X̃1A′ electronic transition in formyl chloride, CHClO

Abstract The ultraviolet absorption spectrum of formyl chloride has been recorded under conditions of modest resolution, 0.75 nm/mm, and long pathlengths, 96 m. The 314- to 269-nm spectrum proved to have well-defined vibrational fine structure and was assigned to the electron promotion, n → π ∗ . A comparison of the spectra of CHClO at 25 and −78°C with CDClO led to the assignments: pseudo-origin, ν2, ν4, ν5, and ν6; 32754.7 32775.3 , 1153.8 1092.0 , 633.6 633.4 , 306.3 303.1 , and 779.5 566.5 cm −1 for CHClO CDClO , respectively. A fit of the 60, 62, 63, and 65 levels to those generated from a Gaussian-quadratic model potential yielded a barrier height of 1608.8 cm−1 and an out-of-plane angle of 48.6° for the A state.

Thiocarbonyl spectroscopy: The Ã1A″ ← X̃1A′ and ã3A″ ← X̃1A′ electronic transitions in thioformyl chloride, CHCIS

Abstract Thioformyl chloride has been synthesized by the pyrolysis of chloromethyl methyl sulfide. Both T-S and S-S a 3 A″ ← X 1 A′ and A 1 A″ ← X 1 A′ systems have been observed in absorption under conditions of low resolution, 1.5 nm/mm, and long pathlength, 96 m. The 0-0 origin of the T-S system was placed at 17233.9 cm−1 and the vibrational modes ν 3 ( CS ) ν 5 ( ClCS ) at 865.0 221.1 cm −1 . The origin of the stronger S-S system was observed at 18792.0 cm−1. Quanta of ν2(SCH)/ν3(CS)/ν4(CCl)/ν5(ClCS)/ν6 (wag) were found at 1338.7/848.0/556.3/230.2/119.7 cm−1. A barrier height of 616.3 cm−1 was obtained for the A 1 A″ state from a fit of the vibrational quanta of a Gaussian-quadratic double minimum function to the 60, 61, 62, 63 levels of the inversion manifold.

Thiocyclopentanone (cyclopentanethione): A vibrational analysis of the Ã1A2 ← X̃1A1 and ã3A2 ← X̃1A1 absorption systems

Abstract The visible absorption spectrum of thiocyclopentanone C 5 H 8 S has been photographically recorded in the vapor phase at long path lengths (56 m). Excitation spectra were obtained over the 530- to 590-nm region with a N 2 pumped dye laser. The lower part of the spectrum was attributed to the spin-forbidden a 3 A 2 ← X 1 A 1 n → π ∗ electronic transition. This system has an open vibational fine structure and was characterized by the activity of a single vibrational mode, ν(CS) = 716.7 cm −1 , which was attached to a strong origin band at 17 050.9 cm −1 . The remainder of the visible spectrum, at shorter wavelengths, was complex. It was assigned to the spin-allowed companion transition, A 1 A 2 ← X 1 A 1 . The origin of this system was the weak band centered at 18 072.4 cm −1 . This spectrum was interpreted in terms of the ring twisting mode ν ″ 18 = 236.2 cm −1 , ν ′ 18 = 251.8 cm −1 , the ring flapping mode, ν ″ 26 = 92.0 cm −1 , ν ′ 26 = 89.1 cm −1 , the sulfur wagging mode ν ′ 25 = 175.0 cm −1 , the CH stretching mode ν ′ 12 = 2980.8 cm −1 , and the CS stretching mode ν ′ 9 = 700.8 cm −1 . The similarity of the ring modes in the X and A states suggests that the ring conformation does not change on electronic excitation.

A vibronic analysis of the lower Ã1A″ ← X̃1A′ singlet-singlet and ã3A″ ← X̃1A′ triplet-singlet band systems of thiopropynal

Abstract The visible absorption spectrum of thiopropynal has been photographed under conditions of long path length, 168 m, and modest dispersion, 15 nm cm−1. Two electronic transitions have been identified in the spectrum. These are the a 3 A″ ← X 1 A′ , triplet-singlet transition which has an origin at 13257.4 cm−1, and the A 1 A″ ← X 1 A′ singlet-singlet transition at 14656.4 cm−1. The vibrational fine structure in both systems is clearly resolved and the bands of triplet multiplicity can be easily distinguished from the singlet bands. Vibrational assignments were made in terms of ν(CCC), ν(CS), ν(CH rock), ν(CC), and ν(CH) out-of-plane.