Communication: Spectroscopic characterization of an alkyl substituted Criegee intermediate syn-CH3CHOO through pure rotational transitions

Abstract

An alkyl-substituted Criegee intermediate syn-CH3CHOO was detected in the gas phase through Fourier-transform microwave spectroscopy. Observed pure rotational transitions show a small splitting corresponding to the A∕E components due to the threefold methyl internal rotation. The rotational constants and the barrier height of the hindered methyl rotation were determined to be A = 17 586.5295(15) MHz, B = 7133.4799(41) MHz, C = 5229.1704(40) MHz, and V3 = 837.1(17) cm(-1). High-level ab initio calculations which reproduce the experimentally determined values well indicate that the in-plane C-H bond in the methyl moiety is trans to the C-O bond, and other two protons are directed to the terminal oxygen atom for the most stable structure of syn-CH3CHOO. The torsional barrier of the methyl top is fairly large in syn-CH3CHOO, implying a significant interaction between the terminal oxygen and the protons of the methyl moiety, which may be responsible for the high production yields of the OH radical from energized alkyl-substituted Criegee intermediates.

Ab initio computational spectroscopy and vibrational dynamics of polyatomic molecules: Applications to syn and anti-CH3CHOO and NO3

“…The UV absorption spectrum of syn-CH 3-CHOO was reported by Beames et al [43]. Later, the microwave spectrum of syn-CH 3 CHOO was reported by Nakajima and Endo [44]. Rotational constants of the ground vibration state were precisely determined as was an effective barrier height of the internal methyl torsion motion.…”

“…The vibrational spectrum of CH 2 OO was calculated, using the MULTIMODE code and good agreement was achieved with experiment. For CH 3 CHOO, several ab initio calculations of stationary points have been reported [43][44][45], as well as a vibrational perturbation theory analysis and the reaction path relevant to the action spectrum mentioned above [45]. However, no fulldimensional PES and DMS exist for syn and anti CH 3 CHOO.…”

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.…”

“…In addition, Nakajima and Endo detected the hydrogenbonded H 2 O-CH 2 OO and D 2 O-CH 2 OO complexes under jet-cooled conditions. 48 Nakajima and Endo detected also the microwave spectra of alkyl-substituted Criegee intermediate syn-CH 3 CHOO 27 and anti-CH 3 CHOO. 29 The observed pure rotational transitions show a small splitting corresponding to the A/E components due to the threefold methyl internal rotation (torsion).…”

“…For CH 3 CHOO, precursor CH 3 CHI 2 was either irradiated with UV light 15,25 or decomposed through electric discharge 27,29 before reaction with O 2 . For (CH 3 ) 2 COO and C 2 H 5 CHOO, precursors 2,2-diiodopropane (CH 3 ) 2 CI 2 and 1,1-diiodopropane C 2 H 5 CHI 2 were applied with a similar mechanism.…”