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

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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 ... continued below

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Howle, Chris R.; Arrowsmith, Alan N.; Chikan, Viktor & Leone,Stephen R. January 18, 2007.

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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.

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  • Journal Name: Journal of Physical Chemistry A; Journal Volume: 111; Journal Issue: 29; Related Information: Journal Publication Date: 03/20/2007

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  • Report No.: LBNL--62529
  • Grant Number: DE-AC02-05CH11231
  • Grant Number: NASA:NNG06GF26G
  • DOI: 10.1021/jp068544w | External Link
  • Office of Scientific & Technical Information Report Number: 922727
  • Archival Resource Key: ark:/67531/metadc893008

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  • January 18, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Sept. 29, 2016, 7:03 p.m.

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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, article, January 18, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc893008/: accessed October 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.