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Title: Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels (X {sup 2}{sigma}{sup +}, v=2, N=0, 1, 6, 10, 15, and 20) and C{sub 2}H{sub 2}

Abstract

Rate coefficients (k{sub tot,N{sub i}}) are reported (a) for total removal (reactive+inelastic) of CN(X {sup 2}{sigma}{sup +},v=2,N{sub i}) radicals from selected rotational levels (N{sub i}=0, 1, 6, 10, 15, and 20) and (b) for state-to-state rotational energy transfer (k{sub i{yields}}{sub f}) between levels N{sub i} and other rotational levels N{sub f} in collisions with C{sub 2}H{sub 2}. CN radicals were generated by pulsed laser photolysis of NCNO at 573 nm. A fraction of the radicals was then promoted to a selected rotational level in v=2 using a tunable infrared ''pump'' laser operating at {approx}2.45 {mu}m, and the subsequent fate of this subset of radicals was monitored using pulsed laser-induced fluorescence (PLIF). Values of k{sub tot,N{sub i}} were determined by observing the decay of the PLIF signals as the delay between pump and probe laser pulses was systematically varied. In a second series of experiments, double resonance spectra were recorded at a short delay between the pump and probe laser pulses. Analysis of these spectra yielded state-to-state rate coefficients for rotational energy transfer, k{sub i{yields}}{sub f}. The difference between the sum of these rate coefficients, {sigma}{sub f}k{sub i{yields}}{sub f}, and the value of k{sub tot,N{sub i}} for the same level N{submore » i} is attributed to the occurrence of chemical reaction, yielding values of the rotationally selected rate coefficients (k{sub reac,N{sub i}}) for reaction of CN from specified rotational levels. These rate coefficients decrease from (7.9{+-}2.2)x10{sup -10} cm{sup 3}molecule{sup -1} s{sup -1} for N{sub i}=0 to (0.8{+-}1.3)x10{sup -10} cm{sup 3} molecule{sup -1} s{sup -1} for N{sub i}=20. The results are briefly discussed in the context of microcanonical transition state theory and the statistical adiabatic channel model.« less

Authors:
;  [1]
  1. University Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW (United Kingdom)
Publication Date:
OSTI Identifier:
20991244
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 13; Other Information: DOI: 10.1063/1.2715594; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CARBON NITRIDES; ENERGY TRANSFER; FLUORESCENCE; LASER RADIATION; MOLECULE-MOLECULE COLLISIONS; ORGANIC COMPOUNDS; PHOTOLYSIS; PULSED IRRADIATION; RADICALS; REACTION KINETICS; ROTATIONAL STATES; SPECTRA

Citation Formats

Olkhov, Rouslan V., and Smith, Ian W. M.. Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels (X {sup 2}{sigma}{sup +}, v=2, N=0, 1, 6, 10, 15, and 20) and C{sub 2}H{sub 2}. United States: N. p., 2007. Web. doi:10.1063/1.2715594.
Olkhov, Rouslan V., & Smith, Ian W. M.. Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels (X {sup 2}{sigma}{sup +}, v=2, N=0, 1, 6, 10, 15, and 20) and C{sub 2}H{sub 2}. United States. doi:10.1063/1.2715594.
Olkhov, Rouslan V., and Smith, Ian W. M.. Sat . "Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels (X {sup 2}{sigma}{sup +}, v=2, N=0, 1, 6, 10, 15, and 20) and C{sub 2}H{sub 2}". United States. doi:10.1063/1.2715594.
@article{osti_20991244,
title = {Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels (X {sup 2}{sigma}{sup +}, v=2, N=0, 1, 6, 10, 15, and 20) and C{sub 2}H{sub 2}},
author = {Olkhov, Rouslan V. and Smith, Ian W. M.},
abstractNote = {Rate coefficients (k{sub tot,N{sub i}}) are reported (a) for total removal (reactive+inelastic) of CN(X {sup 2}{sigma}{sup +},v=2,N{sub i}) radicals from selected rotational levels (N{sub i}=0, 1, 6, 10, 15, and 20) and (b) for state-to-state rotational energy transfer (k{sub i{yields}}{sub f}) between levels N{sub i} and other rotational levels N{sub f} in collisions with C{sub 2}H{sub 2}. CN radicals were generated by pulsed laser photolysis of NCNO at 573 nm. A fraction of the radicals was then promoted to a selected rotational level in v=2 using a tunable infrared ''pump'' laser operating at {approx}2.45 {mu}m, and the subsequent fate of this subset of radicals was monitored using pulsed laser-induced fluorescence (PLIF). Values of k{sub tot,N{sub i}} were determined by observing the decay of the PLIF signals as the delay between pump and probe laser pulses was systematically varied. In a second series of experiments, double resonance spectra were recorded at a short delay between the pump and probe laser pulses. Analysis of these spectra yielded state-to-state rate coefficients for rotational energy transfer, k{sub i{yields}}{sub f}. The difference between the sum of these rate coefficients, {sigma}{sub f}k{sub i{yields}}{sub f}, and the value of k{sub tot,N{sub i}} for the same level N{sub i} is attributed to the occurrence of chemical reaction, yielding values of the rotationally selected rate coefficients (k{sub reac,N{sub i}}) for reaction of CN from specified rotational levels. These rate coefficients decrease from (7.9{+-}2.2)x10{sup -10} cm{sup 3}molecule{sup -1} s{sup -1} for N{sub i}=0 to (0.8{+-}1.3)x10{sup -10} cm{sup 3} molecule{sup -1} s{sup -1} for N{sub i}=20. The results are briefly discussed in the context of microcanonical transition state theory and the statistical adiabatic channel model.},
doi = {10.1063/1.2715594},
journal = {Journal of Chemical Physics},
number = 13,
volume = 126,
place = {United States},
year = {Sat Apr 07 00:00:00 EDT 2007},
month = {Sat Apr 07 00:00:00 EDT 2007}
}
  • The reaction of the cyano radical (CN) with ethane was studied using time-resolved infrared absorption spectroscopy to monitor individual rovibrational states of the HCN product. A method is described that can be used to determine the initial vibrational state distribution at pressures of several Torr. This technique was applied to the title reaction to determine that the vibrational states of HCN({ital v}{sub 1},0,{ital v}{sub 3}), where {ital v}{sub 1}, {ital v}{sub 3}=0, 1, and 2, were {ital not} directly populated in the title reaction to any significant extent. The initial vibrational energy content of the CN radical was also variedmore » but did not influence the initial population in the HCN vibrational levels probed in this experiment. The time dependence of HCN({ital v}{sub 1},0,{ital v}{sub 3}) was followed and interpreted in terms of bimolecular rate constants for vibrational relaxation with ethane. The title reaction is mode specific in its energy disposal in that at least every HCN product appears to have at least one quantum of bending excitation, likely in combination with stretching vibrations.« less
  • The cross sections of spin-orbit energy exchange between the cesium 6 {sup 2}P{sub 1/2}{r_reversible}6 {sup 2}P{sub 3/2} states induced by collisions with N{sub 2}, H{sub 2}, HD, D{sub 2}, CH{sub 4}, C{sub 2}H{sub 6}, CF{sub 4}, and C{sub 2}F{sub 6} were obtained for pressures less than 100 Torr at room temperature by means of steady-state laser-induced fluorescence techniques. The spin-orbit energy exchange rate with N{sub 2}, H{sub 2}, HD, D{sub 2}, CH{sub 4}, C{sub 2}H{sub 6}, CF{sub 4}, and C{sub 2}F{sub 6}, have been measured as {sigma}{sub 21}(6 {sup 2}P{sub 3/2}{yields}6 {sup 2}P{sub 1/2})= 16.3, 34.1, 30.0, 22.7, 21.4, 65.6,more » 64.8, and 137 A{sup 2} and {sigma}{sub 12}(6 {sup 2}P{sub 1/2}{yields}6 {sup 2}P{sub 3/2})= 1.8, 4.4, 4.1, 3.0, 2.9, 13.3, 9.7, and 16.3 A{sup 2}, respectively. Correlations of the spin-orbit transfer probabilities with rotational-energy defect and vibrational-energy defect have been shown.« less
  • By employing the newly established vacuum ultraviolet laser pulsed field ionization-photoion (PFI-PI) double quadrupole-double octopole ion guide apparatus, we have measured the rovibrationally selected absolute total cross sections of the ion-molecule reaction H{sub 2}O{sup +}(X{sup 2}B{sub 1}; v{sub 1}{sup +}v{sub 2}{sup +}v{sub 3}{sup +}= 000; N{sup +}{sub Ka+Kc+)}+ D{sub 2}{yields} H{sub 2}DO{sup +}+ D in the center-of-mass collision energy (E{sub cm}) range of 0.05-10.00 eV. The pulsing scheme used for the generation of PFI-PIs has made possible the preparation of reactant H{sub 2}O{sup +}(X{sup 2}B{sub 1}; v{sub 1}{sup +}v{sub 2}{sup +}v{sub 3}{sup +}= 000) ions in single N{sup +}{sub Ka+Kc+}more » rotational levels with high kinetic energy resolutions. The absolute total cross sections observed in different N{sup +}{sub Ka+Kc+} levels with rotational energies in the range of 0-200 cm{sup -1} were found to exhibit a significant rotational enhancement on the reactivity for the titled reaction. In contrast, the measured cross sections reveal a decreasing trend with increasing E{sub cm}, indicating that the rotational enhancement observed is not a total energy effect, but a dynamical effect. Furthermore, the rotational enhancement is found to be more pronounced as E{sub cm} is decreased. This experiment provided evidence that the coupling of the core rotational angular momentum with the orbital angular momentum could play a role in chemical reactivity, particularly at low E{sub cm}.« less
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  • The vibrational level distribution of the CO(a {sup 3}II) produced in the title reaction was measured in a rapidly pumped discharge-flow reactor at a total pressure of {approximately}2 Torr and {approximately}297 K. The emission from the CO(a {sup 3}II,v{sup {prime}}{r_arrow}X {sup 1}{Sigma}{sup +}, v{sup {prime}{prime}}) Cameron bands, observed from the product CO(a) formed in the title reaction, was collected with a 2.2-m vacuum-ultraviolet spectrograph-monochromator utilizing both photographic and photoelectric techniques. For N{sub 2}(A,v{sup {prime}}{le}4) + CO(X,v{sup {prime}{prime}}=O) the authors obtain a CO(a,v{sup {prime}}) population ratio of 1.00:0.85 for v{sup {prime}} = 0 and 1, respectively. This branching ratio differs frommore » previous results for N{sub 2}(A,v{sup {prime}}{ge}0) which did not correct for competing removal processes of the CO(a) state. In order to obtain these results it was necessary to measure the room temperature biomolecular rate constants, k{sub v}{sup {prime}}`s, for the CO(a,v{sup {prime}}=0 and 1) + CF{sub 4} reactions which were determined to be {le}5 x 10{sup {minus}14} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. 31 refs., 1 tab.« less