UV spectroscopic characterization of an alkyl substituted Criegee intermediate CH3CHOO

Abstract

Ozonolysis of alkenes in the troposphere proceeds through a Criegee intermediate, or carbonyl oxide, which has only recently been detected in the gas phase. The present study focuses on the production of an alkyl-substituted Criegee intermediate, CH3CHOO, in a pulsed supersonic expansion, and then utilizes VUV photoionization at 118 nm and UV-induced depletion of the m∕z = 60 signal to probe the B (1)A(') ← X (1)A(') transition. The UV-induced depletion approaches 100% near the peak of the profile at 320 nm, indicating rapid dynamics in the B state, and corresponds to a peak absorption cross section of ∼5 × 10(-17) cm(2) molecule(-1). The electronic spectrum for CH3CHOO is similar to that reported recently for CH2OO, but shifted 15 nm to shorter wavelength, which will result in a longer tropospheric lifetime for CH3CHOO with respect to solar photolysis. Complementary electronic structure calculations (EOM-CCSD) are carried out for the B and X potentials of these Criegee intermediates along the O-O coordinate. An intramolecular interaction stabilizes the ground state of the syn-conformer of CH3CHOO relative to anti-CH3CHOO, and indicates that the syn-conformer will be the more abundant species in the expansion. The excited B electronic state of syn-CH3CHOO is also predicted to be destabilized relative to that for anti-CH3CHOO and CH2OO, in accord with the shift in the B-X transition observed experimentally. Hydroxyl radicals produced concurrently with the generation of the Criegee intermediates are detected by 1+1(') resonance enhanced multiphoton ionization. The OH yield observed with CH3CHOO is 4-fold larger than that from CH2OO, consistent with prior studies of OH generation from alkene ozonolysis.

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

“…After the discovery of this source of CH 2 OO, many researchers utilized this scheme to produce CH 2 OO and reported ultraviolet (UV) depletion, 18 UV absorption, 19,20 infrared (IR) absorption, 21 microwave, 22,23 and submillimeter-wave 24 spectra. Spectra of slightly larger Criegee intermediates such as acetaldehyde oxide (CH 3 CHOO), 15,[25][26][27][28][29][30][31][32] acetone oxide [(CH 3 ) 2 COO], 16,33 and propionaldehyde oxide (C 2 H 5 CHOO) 10 are also reported. Figure 1 shows the structures of CH 2 OO, syn-CH 3 CHOO, and anti-CH 3 CHOO.…”

The UV absorption spectrum of the simplest Criegee intermediate CH2OO

“…Now it is generally accepted that ozonolysis of alkenes proceeds via Criegee intermediates, highly reactive species postulated in 1949 by Rudolf Criegee. 1,2 In the troposphere, Criegee intermediates are involved in several important atmospheric reactions, 3 including reactions with SO 2 and NO 2 , [4][5][6][7] or can be photolyzed by near UV light, [7][8][9][10] as shown for CH 2 The formation of SO 3 and NO 3 , as in (R2) and (R3), plays an important role in atmospheric chemistry, 11,12 including aerosol and cloud formation. The formation of O( 1 D), as in (R4), will result in OH formation through (R5).…”

UV photodissociation dynamics of CHI2Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate

“…[41][42][43][44] Photolysis of larger geminal diiodoalkanes to produce iodoalkyl radicals which can subsequently react with O2 has been used successfully to produce larger Criegee intermediates. 45,46 While the major source of most Criegee intermediates in the atmosphere is alkene ozonolysis, the photolytic production of iodoalkyl radicals could also contribute in regions such as the MBL where precursor concentrations are elevated. Halogen-substituted alkenes react extremely slowly with ozone, with rate constants typically <10 -19 cm 3 molecules -1 .…”