Ultraviolet photochemistry of trichlorovinylsilane and allyltrichlorosilane: vinyl radical (HCCH2) and allyl radical (H2CCHCH2) production in 193 nm photolysis

Abstract

The absolute gas phase ultraviolet absorption spectra of trichlorovinylsilane and allyltrichlorosilane have been measured from 191 to 220 nm. Over this region the absorption spectra of both species are broad and relatively featureless, and their cross sections increase with decreasing wavelength. The electronic transitions of trichlorovinylsilane were calculated by ab initio quantum chemical methods and the observed absorption bands assigned to the A(1)A''<-- X[combining tilde](1)A'' transition. The maximum absorption cross section in the region, at 191 nm, is sigma = (8.50 +/- 0.06) x 10(-18) cm(2) for trichlorovinylsilane and sigma = (2.10 +/- 0.02) x 10(-17) cm(2) for allyltrichlorosilane. The vinyl radical and the allyl radical are formed promptly from the 193 nm photolysis of their respective trichlorosilane precursors. By comparison of the transient visible absorption and the 1315 nm I atom absorption from 266 nm photolysis of vinyl iodide and allyl iodide, the absorption cross sections at 404 nm of vinyl radical ((2.9 +/- 0.4) x 10(-19) cm(2)) and allyl radical ((3.6 +/- 0.8) x 10(-19) cm(2)) were derived. These cross sections are in significant disagreement with literature values derived from kinetic modeling of allyl or vinyl radical self-reactions. Using these cross sections, the vinyl radical yield from trichlorovinylsilane was determined to be phi = (0.9 +/- 0.2) per 193 nm photon absorbed, and the allyl radical yield from allyltrichlorosilane phi = (0.7 +/- 0.2) per 193 nm photon absorbed.

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

“…However, the TR-BB-CEAS technique enables a clean deconvolution of vinyl radical decay from IO formation. [15][16][17], and overall the agreement with expected initial radical concentration is excellent. …”

“…The vinyl radical is one of the simplest unsaturated hydrocarbon radicals and is of central importance in combustion and planetary atmospheric processes. It has a well-characterized absorption band in the 400 -530 nm range (the A 2 A″ ← X 2 A′ transition) with an extensive vibrational progression and a moderate absorption cross-section (~ 3•10 -19 cm 2 at 404 nm) [15][16][17]. In the presence of O 2 the main decay pathways of the vinyl radical are shown below [14,18] …”

Formation of Trichlorosilyl‐Substituted Carbon‐Centered Stable Radicals through the Use of π‐Accepting Carbenes

“…9a and its congener SiCl 3 . 9b are frequently generated by flash photolysis. These species are active radical intermediates in many photochemical transformations 9a,b.…”

Yield of Formyl Radical from the Vinyl + O2 Reaction

“…These values are in reasonable agreement with the presently employed value considering the low spectral resolution of Hunziker et al (1.6 nm) and the estimated uncertainties. DeSain et al reported σ vinyl,404 of (2.9 ± 0.4) × 10 −19 cm −2 , which is slightly larger than the value given by Ismail et al . As mentioned by Ismail et al, this discrepancy may partly arise from the differences in the frequency resolution of the probe lasers used (0.2 nm of Ismail et al compared to 1 nm of DeSain et al ).…”

“…As mentioned by Ismail et al, this discrepancy may partly arise from the differences in the frequency resolution of the probe lasers used (0.2 nm of Ismail et al compared to 1 nm of DeSain et al ). It should be noted that the absorption cross section of allyl radical at approximately 404 nm estimated by DeSain et al was also larger than the recently determined value by using the present PLP/CRDS apparatus .…”