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Title: Velocity map imaging of O-atom products from UV photodissociation of the CH{sub 2}OO Criegee intermediate

Abstract

UV excitation of jet-cooled CH{sub 2}OO X{sup 1}A′ to the excited B{sup 1}A′ electronic states results in dissociation to two spin-allowed product channels: H{sub 2}CO X{sup 1}A{sub 1} + O {sup 1}D and H{sub 2}CO a{sup 3}A″ + O {sup 3}P. In this study, the higher energy H{sub 2}CO a{sup 3}A″ + O {sup 3}P channel is characterized by velocity map imaging and UV action spectroscopy, in both cases utilizing 2 + 1 resonance enhanced multiphoton ionization detection of O {sup 3}P products, which complements a prior experimental study on the lower energy H{sub 2}CO X{sup 1}A{sub 1} + O {sup 1}D channel [Lehman et al., J. Chem. Phys. 139, 141103 (2013)]. Anisotropic angular distributions indicative of rapid dissociation are obtained at 330 and 350 nm, along with broad and unstructured total kinetic energy distributions that provide insight into the internal excitation of the H{sub 2}CO a{sup 3}A″ co-fragment. A harmonic normal mode analysis points to significant vibrational excitation of the CH{sub 2} wag and C–O stretch modes of the H{sub 2}CO a{sup 3}A″ fragment upon dissociation. At each UV wavelength, the termination of the kinetic energy distribution reveals the energetic threshold for the H{sub 2}CO a{sup 3}A″ + Omore » {sup 3}P product channel of ca. 76 kcal mol{sup −1} (378 nm) and also establishes the dissociation energy from CH{sub 2}OO X{sup 1}A′ to H{sub 2}CO X{sup 1}A{sub 1} + O{sup 1}D products of D{sub 0} ≤ 49.0 ± 0.3 kcal mol{sup −1}, which is in accord with prior theoretical studies. The threshold for the H{sub 2}CO a{sup 3}A″ + O {sup 3}P channel is also evident as a more rapid falloff on the long wavelength side of the O {sup 3}P action spectrum as compared to the previously reported UV absorption spectrum for jet-cooled CH{sub 2}OO [Beames et al., J. Am. Chem. Soc. 134, 20045 (2012)]. Modeling suggests that the O {sup 3}P yield increases uniformly from 378 to 300 nm.« less

Authors:
; ;
Publication Date:
OSTI Identifier:
22415941
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 142; Journal Issue: 21; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTRA; ANGULAR DISTRIBUTION; ATOMS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DISSOCIATION; DISSOCIATION ENERGY; EXCITATION; KINETIC ENERGY; NORMAL-MODE ANALYSIS; PHOTOIONIZATION; PHOTOLYSIS; RESONANCE; SPIN; YIELDS

Citation Formats

Li, Hongwei, Fang, Yi, Beames, Joseph M., and Lester, Marsha I., E-mail: milester@sas.upenn.edu. Velocity map imaging of O-atom products from UV photodissociation of the CH{sub 2}OO Criegee intermediate. United States: N. p., 2015. Web. doi:10.1063/1.4921990.
Li, Hongwei, Fang, Yi, Beames, Joseph M., & Lester, Marsha I., E-mail: milester@sas.upenn.edu. Velocity map imaging of O-atom products from UV photodissociation of the CH{sub 2}OO Criegee intermediate. United States. doi:10.1063/1.4921990.
Li, Hongwei, Fang, Yi, Beames, Joseph M., and Lester, Marsha I., E-mail: milester@sas.upenn.edu. Sun . "Velocity map imaging of O-atom products from UV photodissociation of the CH{sub 2}OO Criegee intermediate". United States. doi:10.1063/1.4921990.
@article{osti_22415941,
title = {Velocity map imaging of O-atom products from UV photodissociation of the CH{sub 2}OO Criegee intermediate},
author = {Li, Hongwei and Fang, Yi and Beames, Joseph M. and Lester, Marsha I., E-mail: milester@sas.upenn.edu},
abstractNote = {UV excitation of jet-cooled CH{sub 2}OO X{sup 1}A′ to the excited B{sup 1}A′ electronic states results in dissociation to two spin-allowed product channels: H{sub 2}CO X{sup 1}A{sub 1} + O {sup 1}D and H{sub 2}CO a{sup 3}A″ + O {sup 3}P. In this study, the higher energy H{sub 2}CO a{sup 3}A″ + O {sup 3}P channel is characterized by velocity map imaging and UV action spectroscopy, in both cases utilizing 2 + 1 resonance enhanced multiphoton ionization detection of O {sup 3}P products, which complements a prior experimental study on the lower energy H{sub 2}CO X{sup 1}A{sub 1} + O {sup 1}D channel [Lehman et al., J. Chem. Phys. 139, 141103 (2013)]. Anisotropic angular distributions indicative of rapid dissociation are obtained at 330 and 350 nm, along with broad and unstructured total kinetic energy distributions that provide insight into the internal excitation of the H{sub 2}CO a{sup 3}A″ co-fragment. A harmonic normal mode analysis points to significant vibrational excitation of the CH{sub 2} wag and C–O stretch modes of the H{sub 2}CO a{sup 3}A″ fragment upon dissociation. At each UV wavelength, the termination of the kinetic energy distribution reveals the energetic threshold for the H{sub 2}CO a{sup 3}A″ + O {sup 3}P product channel of ca. 76 kcal mol{sup −1} (378 nm) and also establishes the dissociation energy from CH{sub 2}OO X{sup 1}A′ to H{sub 2}CO X{sup 1}A{sub 1} + O{sup 1}D products of D{sub 0} ≤ 49.0 ± 0.3 kcal mol{sup −1}, which is in accord with prior theoretical studies. The threshold for the H{sub 2}CO a{sup 3}A″ + O {sup 3}P channel is also evident as a more rapid falloff on the long wavelength side of the O {sup 3}P action spectrum as compared to the previously reported UV absorption spectrum for jet-cooled CH{sub 2}OO [Beames et al., J. Am. Chem. Soc. 134, 20045 (2012)]. Modeling suggests that the O {sup 3}P yield increases uniformly from 378 to 300 nm.},
doi = {10.1063/1.4921990},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 21,
volume = 142,
place = {United States},
year = {2015},
month = {6}
}