Low-temperature rate coefficients of C{sub 2}H with CH{sub 4} and CD{sub 4} from 154 to 359 K
- National Inst. of Standards and Technology, Boulder, CO (United States)
Rate coefficients for the reaction C{sub 2}H + CH{sub 4} {yields} C{sub 2}H{sub 2} + CH{sub 3} and C{sub 2}H + CD{sub 4} {yields} C{sub 2}HD + CD{sub 3} are measured over the temperature range 154-359 K using transient infrared laser absorption spectroscopy. Ethynyl radicals are produced by pulsed laser photolysis of C{sub 2}H{sub 2} in a variable temperature flow cell, and a tunable color center laser probes the transient removal of C{sub 2}H (X{sup 2}{Sigma}{sup +} (0,0,0)) in absorption. The rate coefficients for the reactions of C{sub 2}H with CH{sub 4} and CD{sub 4} both show a positive temperature dependence over the range 154-359 K, which can be expressed as k{sub CH(4)} = (1.2{+-}0.1) x 10{sup -11} exp[(-149{+-}12)/T] and k{sub CD(4)} = (8.7{+-}1.8) x 10{sup -12} exp[(-650{+-}61)/T] cm{sup 3} molecule{sup -1} s{sup -1}, respectively. The reaction of C{sub 2}H + CH{sub 4} exhibits a significant kinetic isotope effect at 300 K of k{sub CH(4)}/k{sub CD(4)} = 2.5{+-}0.2. Temperature dependent rate constants for C{sub 2}H + C{sub 2}H{sub 2} were also remeasured over an increased temperature range from 143 to 359 K and found to show a slight negative temperature dependence, which can be expressed as k{sub C(2)H(2)} = 8.6 x 10{sup -16} T{sup 1.8} exp[(474{+-}90)/T] cm{sup 3} molecule{sup -1} s{sup -1}. 71 refs., 6 figs., 3 tabs.
- OSTI ID:
- 232515
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 12 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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