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Title: State-Resolved Dynamics of the CN(B2Sigma+) and CH(A2Delta)Excited Products Resulting from the VUV Photodissociation of CH3CN

Abstract

Fourier transform visible spectroscopy, in conjunction withVUV photons produced by a synchrotron, is employed to investigate thephotodissociation of CH3CN. Emission is observed from both theCN(B2Sigma+ - X2Sigma+) and CH(A2Delta - X2PI) transitions; only theformer is observed in spectra recorded at 10.2 and 11.5 eV, whereas bothare detected in the 16 eV spectrum. The rotational and vibrationaltemperatures of both the CN(B2Sigma+) and CH(A2Delta) radical productsare derived using a combination of spectral simulations and Boltzmannplots. The CN(B2Sigma+) fragment displays a bimodal rotationaldistribution in all cases. Trot(CN(B2Sigma+)) ranges from 375 to 600 K atlower K' and from 1840 to 7700 K at higher K' depending on the photonenergy used. Surprisal analyses indicate clear bimodal rotationaldistributions, suggesting CN(B2Sigma+) is formed via either linear orbent transition states, respectively, depending on the extent ofrotational excitation in this fragment. CH(A2Delta) has a singlerotational distribution when produced at 16 eV which results inTrot(CH(A2Delta)) = 4895 +- 140 K in nu' = 0 and 2590 +- 110 K in nu' =1. From thermodynamic calculations, it is evident that CH(A2Delta) isproduced along with CN(X2Sigma+) + H2. These products can be formed by atwo step mechanism (via excited CH3* and ground state CN(X2Sigma+) or aprocess similar to the "roaming" atom mechanism;more » the data obtained hereare insufficient to definitively conclude whether either pathway occurs.A comparison of the CH(A2Delta) and CN(B2Sigma+) rotational distributionsproduced by 16 eV photons allows the ratio between the two excitedfragments at this energy to be determined. An expression that considersthe rovibrational populations of both band systems results in aCH(A2Delta):CN(B2Sigma+) ratio of (1.2 +- 0.1):1 at 16 eV, therebyindicating that production of CH(A2Delta) is significant at 16eV.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Director, Office of Science. Office of Basic EnergySciences; National Aeronautics and Space Administration
OSTI Identifier:
922727
Report Number(s):
LBNL-62529
R&D Project: 401001; BnR: KC0301020; TRN: US0801743
DOE Contract Number:  
DE-AC02-05CH11231; NASA:NNG06GF26G
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A; Journal Volume: 111; Journal Issue: 29; Related Information: Journal Publication Date: 03/20/2007
Country of Publication:
United States
Language:
English
Subject:
74; ATOMS; DISTRIBUTION; EXCITATION; GROUND STATES; PHOTONS; PRODUCTION; RADICALS; SPECTRA; SPECTROSCOPY; THERMODYNAMICS; Titan interstellar medium combustion Fourier transformspectroscopy

Citation Formats

Howle, Chris R., Arrowsmith, Alan N., Chikan, Viktor, and Leone,Stephen R.. State-Resolved Dynamics of the CN(B2Sigma+) and CH(A2Delta)Excited Products Resulting from the VUV Photodissociation of CH3CN. United States: N. p., 2007. Web. doi:10.1021/jp068544w.
Howle, Chris R., Arrowsmith, Alan N., Chikan, Viktor, & Leone,Stephen R.. State-Resolved Dynamics of the CN(B2Sigma+) and CH(A2Delta)Excited Products Resulting from the VUV Photodissociation of CH3CN. United States. doi:10.1021/jp068544w.
Howle, Chris R., Arrowsmith, Alan N., Chikan, Viktor, and Leone,Stephen R.. Thu . "State-Resolved Dynamics of the CN(B2Sigma+) and CH(A2Delta)Excited Products Resulting from the VUV Photodissociation of CH3CN". United States. doi:10.1021/jp068544w. https://www.osti.gov/servlets/purl/922727.
@article{osti_922727,
title = {State-Resolved Dynamics of the CN(B2Sigma+) and CH(A2Delta)Excited Products Resulting from the VUV Photodissociation of CH3CN},
author = {Howle, Chris R. and Arrowsmith, Alan N. and Chikan, Viktor and Leone,Stephen R.},
abstractNote = {Fourier transform visible spectroscopy, in conjunction withVUV photons produced by a synchrotron, is employed to investigate thephotodissociation of CH3CN. Emission is observed from both theCN(B2Sigma+ - X2Sigma+) and CH(A2Delta - X2PI) transitions; only theformer is observed in spectra recorded at 10.2 and 11.5 eV, whereas bothare detected in the 16 eV spectrum. The rotational and vibrationaltemperatures of both the CN(B2Sigma+) and CH(A2Delta) radical productsare derived using a combination of spectral simulations and Boltzmannplots. The CN(B2Sigma+) fragment displays a bimodal rotationaldistribution in all cases. Trot(CN(B2Sigma+)) ranges from 375 to 600 K atlower K' and from 1840 to 7700 K at higher K' depending on the photonenergy used. Surprisal analyses indicate clear bimodal rotationaldistributions, suggesting CN(B2Sigma+) is formed via either linear orbent transition states, respectively, depending on the extent ofrotational excitation in this fragment. CH(A2Delta) has a singlerotational distribution when produced at 16 eV which results inTrot(CH(A2Delta)) = 4895 +- 140 K in nu' = 0 and 2590 +- 110 K in nu' =1. From thermodynamic calculations, it is evident that CH(A2Delta) isproduced along with CN(X2Sigma+) + H2. These products can be formed by atwo step mechanism (via excited CH3* and ground state CN(X2Sigma+) or aprocess similar to the "roaming" atom mechanism; the data obtained hereare insufficient to definitively conclude whether either pathway occurs.A comparison of the CH(A2Delta) and CN(B2Sigma+) rotational distributionsproduced by 16 eV photons allows the ratio between the two excitedfragments at this energy to be determined. An expression that considersthe rovibrational populations of both band systems results in aCH(A2Delta):CN(B2Sigma+) ratio of (1.2 +- 0.1):1 at 16 eV, therebyindicating that production of CH(A2Delta) is significant at 16eV.},
doi = {10.1021/jp068544w},
journal = {Journal of Physical Chemistry A},
number = 29,
volume = 111,
place = {United States},
year = {Thu Jan 18 00:00:00 EST 2007},
month = {Thu Jan 18 00:00:00 EST 2007}
}