Visible Absorption Spectrum of the CH₃CO Radical

Abstract

The visible absorption spectrum of the acetyl radical, CH(3)CO, was measured between 490 and 660 nm at 298 K using cavity ring-down spectroscopy. Gas-phase CH(3)CO radicals were produced using several methods including: (1) 248 nm pulsed laser photolysis of acetone (CH(3)C(O)CH(3)), methyl ethyl ketone (MEK, CH(3)C(O)CH(2)CH(3)), and biacetyl (CH(3)C(O)C(O)CH(3)), (2) Cl + CH(3)C(O)H --> CH(3)C(O) + HCl with Cl atoms produced via pulsed laser photolysis or in a discharge flow tube, and (3) OH + CH(3)C(O)H --> CH(3)CO + H(2)O with two different pulsed laser photolysis sources of OH radicals. The CH(3)CO absorption spectrum was assigned on the basis of the consistency of the spectra obtained from the different CH(3)CO sources and agreement of the measured rate coefficients for the reaction of the absorbing species with O(2) and O(3) with literature values for the CH(3)CO + O(2) + M and CH(3)CO + O(3) reactions. The CH(3)CO absorption spectrum between 490 and 660 nm has a broad peak centered near 535 nm and shows no discernible structure. The absorption cross section of CH(3)CO at 532 nm was measured to be (1.1 +/- 0.2) x 10(-19) cm(2) molecule(-1) (base e).

Photochemistry of the iron(III) complex with pyruvic acid in aqueous solutions

“…The presence of such bands could be predicted from the fact that in the gas phase the broad band with a maxi mum at 530 nm corresponds to the Me • CO radical. 42 The absorption of the Me • CO radical in organic glasses at 550 nm was reported. 43 However, the authors of this work carried out no quantitative measurements.…”

Kinetic study of the reaction of the acetyl radical, CH3CO, with O3 using cavity ring-down spectroscopy

“…Rate coefficients were measured under pseudo-first-order conditions in CH 3 CO, [CH 3 CO] < [O 3 ], over the temperature range 248-403 K. The experimental apparatus has been used previously in our laboratory [15] and only the details relevant to the present study are described here.…”

“…The CRDS technique is briefly described here and additional details are available in our recent studies of the visible spectrum of CH 3 CO [15], quantum yields of CH 3 CO from the UV photolysis of acetone [4], and rate coefficients for reaction of Cl 2 with CH 3 CO [9]. The CRDS time constant, s, is related to the absorption coefficient, a (cm À1 ) at time t by pathlength, L s is the pathlength of the absorbing species, c is the speed of light, and s t and s 0 are the ring-down time constants with and without the absorber present, respectively.…”

“…The absorption coefficient was measured at variable time delays, t, following the photolysis laser pulse to map out the CH 3 CO temporal profile. The CH 3 CO absorption spectrum in the visible region is continuous between 490 and 660 nm with an absorption cross-section, r, of (1.1 ± 0.2) Â 10 À19 cm 2 molecule À1 at 532 nm [15].…”

“…This study used a crossed pulsed laser photolysis -CRDS setup where the photolysis beam passed through the reaction cell at a right angle to the CRDS optical cavity [9,15]. Side-arms on the reactor allowed the CRD beam to pass through its center.…”