Electronic Spectra of Thioformaldehyde and the Methyl Thiyl Radical

We report the infrared absorption spectrum of the methylthio (or thiomethoxy) radical, CH(3)S (X (2)E(3/2)), produced via photodissociation in situ of three precursors CH(3)SH, CH(3)SCH(3), and CH(3)SSCH(3) isolated in solid p-H(2). The common absorption features observed with similar intensity ratios in each experiment are assigned to CH(3)S. The wavenumbers of these features agree satisfactorily with those predicted with a spin-vibronic Hamiltonian accounting for the anharmonic effects and the Jahn-Teller effects to the quartic term [A. V. Marenich and J. E. Boggs, J. Chem. Theory Comput. 1, 1162 (2005)]. In addition to an absorption line at 724.2 cm(-1), corresponding to a transition of 3(1) previously determined to be 727 cm(-1) from fluorescence spectra of gaseous CH(3)S, we identified fundamental transitions 6(1)(a(1)) at 771.1, 6(1)(e) at 1056.6, 5(1)(a(1)) at 1400.0, 4(1)(a(1)) at 2898.4 cm(-1), and several combination and overtone transitions. In contrast, photolysis of CH(3)SSCH(3) isolated in solid Ar produces mainly H(2)CS, CH(3)SH, and CS(2), but no CH(3)S. These results demonstrate the feasibility of using photolysis in situ of precursors isolated in solid p-H(2) to produce free radicals by taking advantage of the diminished cage effect of the matrix.

Section: Introductionmentioning

confidence: 99%

Diminished cage effect in solid p-H2: Infrared absorption of CH3S observed from photolysis in situ of CH3SH, CH3SCH3, or CH3SSCH3 isolated in p-H2 matrices

Bahou

Lee

2010

“…The methylthio radical has been proposed as an important intermediate in atmospheric oxidation of naturally occurring sulfur species such as dimethyl sulfide (CH 3 SCH 3 ), dimethyl disulfide (CH 3 SSCH 3 ) and methyl mercaptan (CH 3 SH). 4 There have been numerous spectroscopic studies of the methylthio radical since its first spectroscopic observation by Callear and Dickson, 5 a diffuse absorption band centered at 45 770 cm Ϫ1 . Anion photoelectron and photodetachment spectroscopy, 6-8 microwave 9 and infrared spectroscopy, 10 and electronic emission 11 studies have provided information regarding the geometry, spin-orbit splitting and vibrational frequencies of the X 2 E ground state.…”

Section: Introductionmentioning

confidence: 99%

Photodissociation spectroscopy and dynamics of the methylthio radical (CH3S)

Bise

Choi

Pedersen

et al. 1999

The photodissociation spectroscopy and dynamics of the CH 3 S and CD 3 S radicals have been investigated using fast radical beam photofragment spectroscopy of the Ã 2 A 1 ←X 2 E electronic band (T 0 Х26 400 cm Ϫ1) and an unstructured band near 45 600 cm Ϫ1. At all energies, only one major channel, CH 3 (X 2 A 2 Љ)ϩS(3 P j), was observed. Photofragment yield spectra for the Ã 2 A 1 ←X 2 E electronic band show resolved vibrational progressions extending well beyond those seen in laser-induced fluorescence studies of this band. Photofragment translational energy distributions yield the S(3 P j) fine-structure distribution for each vibrational level of the CH 3 product. Photofragment angular distributions were found to be highly anisotropic ͑␤ϭϪ0.2 to Ϫ1.0Ϯ0.1͒ with increasing anisotropy at higher photon energies. The results yield a refined heat of formation for CH 3 S ͑1.346Ϯ0.018 eV͒ as well as the mechanism by which the Ã 2 A 1 state is predissociated. Results at 45 600 cm Ϫ1 imply that dissociation occurs on the repulsive B 2 A 2 state.

“…The corresponding transitions for CH 2 0 are at 5.7 and 6.4X10 4 em-I, respectively.14 The n---t(J* transition in CH 2 S has been confirmed by Call ear et al, who observed an energy difference of 4.7 X 10 4 cm-I . 15 Further evidence for the lower difference energies in thioformaldehyde relative to formaldehyde is found in the thermodynamic work of Jones and Lossing.1 6 All of these lower energy electronic transitions could therefore lead to a larger gaa in CH2S. The fact that the second term for gaa in Eq.…”

Section: Discussionmentioning

confidence: 91%

Molecular Rotational Zeeman Effect in Thioformaldehyde

Rock

Flygare

1972

The high-field rotational Zeeman effect has been observed in thioformaldehyde. The magnetic susceptibility anisotropies are 2Xaa-Xbb-Xcc=S2.3± 1.1 (X 10-j! erg/G2· mole) and 2Xbb-Xaa-Xcc= -S.1± 0.7. The molecular g values with uniquely determined signs are gaa= -S.2602±0.OO68, gbb= -0.1337± 0.0004, and gcc= -0.0239±0.0004. c is the out-of-plane axis and the a axis is the dipole axis. gaa represents the largest molecular g value yet measured. Use of these five Zeeman parameters and the known structure gives the molecular quadrupole moments: Qaa=3.0±0.7(Xto-26 esu·cm 2 ), Qbb=-2.4±0.S, Qcc=-0.6± 1.1; the diagonal elements of the paramagnetic susceptibility tensor: Xaa P = 4S.8±0.3 (X to-6 erg /G2. mole) , xbb P =88.3±0.6, xccP=82.6±0.6; and the anisotropies in the second moments of the electronic charge distribution. By estimating the out-of-plane second moment of the electronic charge distribution as (c 2 )= 4.6±0.4(X 10-16 cml) using free atom values, we have evaluated the remaining individual second moments of the electronic charge distribution to be (a 2 )=21.1±0.6(XlO-lS cm2) and (b 2 )=6.6±0.S. The diagonal elements of the diamagnetic and total magnetic susceptibility tensor also follow from the above estimation of (c 2 ) and are xaa d =-47.5±2.5(XlO-S erg/G2.mole) , Xbb d =-to9.1±3.0, xcc d =-117.6±3.4, Xaa= -1.7±2.S, Xbb= -20.8±3.1, and Xcc= -3S.0±3.S, giving the bulk magnetic susceptibility as x=Hxaa+ Xbb+Xcc) = -19.2±1.8(X 1~ erg/G2.mole). These values are then compared to those of the oxygen analog, formaldehyde, and trends in this pair are compared to several other previously studied oxygensulfur analogs.