{"title":"Rate Coefficients of C2H with C2H4, C2H6, and H2 from 150 to 359 K","authors":"Brian J. Opansky, Stephen R. Leone","doi":"10.1021/jp9619604","DOIUrl":null,"url":null,"abstract":"<p >Rate coefficients for the reactions C<sub>2</sub>H with C<sub>2</sub>H<sub>4</sub>, C<sub>2</sub>H<sub>6</sub>, and H<sub>2</sub> are measured over the temperature range 150?359 K using transient infrared laser absorption spectroscopy. The ethynyl radical is formed by photolysis of C<sub>2</sub>H<sub>2</sub> with a pulsed excimer laser at 193 nm, and its transient absorption is monitored with a color center laser on the Q<sub>11</sub>(9) line of the A<sup>2</sup>Π?X<sup>2</sup>Σ transition at 3593.68 cm<sup>-1</sup>. Over the experimental temperature range 150?359 K the rate constants of C<sub>2</sub>H with C<sub>2</sub>H<sub>4</sub>, C<sub>2</sub>H<sub>6</sub>, and H<sub>2</sub> can be fit to the Arrhenius expressions <i>k</i><sub>C</sub><sub><sub>2</sub></sub><sub>H</sub><sub><sub>4</sub></sub> = (7.8 ± 0.6) × 10<sup>-11</sup> exp[(134 ± 44)/<i>T</i>], <i>k</i><sub>C</sub><sub><sub>2</sub></sub><sub>H</sub><sub><sub>6</sub></sub> = (3.5 ± 0.3) × 10<sup>-11</sup> exp[(2.9 ± 16)/<i>T</i>], and <i>k</i><sub>H</sub><sub><sub>2</sub></sub> = (1.2 ± 0.3) × 10<sup>-11</sup> exp[(?998 ± 57)]/<i>T</i> cm<sup>3</sup> molecule<sup>-1</sup> s<sup>-1</sup>, respectively. The data for C<sub>2</sub>H with C<sub>2</sub>H<sub>4</sub> and C<sub>2</sub>H<sub>6</sub> indicate a negligible activation energy to product formation shown by the mild negative temperature dependence of both reactions. When the H<sub>2</sub> data are plotted together with the most recent high-temperature results from 295 to 854 K, a slight curvature is observed. The H<sub>2</sub> data can be fit to the non-Arrhenius form <i>k</i><sub>H</sub><sub><sub>2</sub></sub> = 9.2 × 10<sup>-18</sup><i>T</i><sup>2.17±0.50</sup> exp[(?478 ± 165)/<i>T</i>] cm<sup>3</sup> molecule<sup>-1</sup> s<sup>-1</sup>. The curvature in the Arrhenius plot is discussed in terms of both quantum mechanical tunneling of the H atom from H<sub>2</sub> to the C<sub>2</sub>H radical and bending mode contributions to the partition function. </p>","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.7810,"publicationDate":"1996-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1021/jp9619604","citationCount":"57","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"The Journal of Physical Chemistry ","FirstCategoryId":"1","ListUrlMain":"https://pubs.acs.org/doi/10.1021/jp9619604","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 57
Abstract
Rate coefficients for the reactions C2H with C2H4, C2H6, and H2 are measured over the temperature range 150?359 K using transient infrared laser absorption spectroscopy. The ethynyl radical is formed by photolysis of C2H2 with a pulsed excimer laser at 193 nm, and its transient absorption is monitored with a color center laser on the Q11(9) line of the A2Π?X2Σ transition at 3593.68 cm-1. Over the experimental temperature range 150?359 K the rate constants of C2H with C2H4, C2H6, and H2 can be fit to the Arrhenius expressions kC2H4 = (7.8 ± 0.6) × 10-11 exp[(134 ± 44)/T], kC2H6 = (3.5 ± 0.3) × 10-11 exp[(2.9 ± 16)/T], and kH2 = (1.2 ± 0.3) × 10-11 exp[(?998 ± 57)]/T cm3 molecule-1 s-1, respectively. The data for C2H with C2H4 and C2H6 indicate a negligible activation energy to product formation shown by the mild negative temperature dependence of both reactions. When the H2 data are plotted together with the most recent high-temperature results from 295 to 854 K, a slight curvature is observed. The H2 data can be fit to the non-Arrhenius form kH2 = 9.2 × 10-18T2.17±0.50 exp[(?478 ± 165)/T] cm3 molecule-1 s-1. The curvature in the Arrhenius plot is discussed in terms of both quantum mechanical tunneling of the H atom from H2 to the C2H radical and bending mode contributions to the partition function.