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High‐temperature collisional energy transfer in highly vibrationally excited molecules II: Isotope effects in isopropyl bromide systems
Author(s) -
Brown Trevor C.,
King Keith D.,
Gilbert Robert G.
Publication year - 1987
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550190906
Subject(s) - chemistry , kinetic isotope effect , excited state , deuterium , bromide , xenon , analytical chemistry (journal) , molecule , kinetic energy , atomic physics , inorganic chemistry , physics , organic chemistry , chromatography , quantum mechanics
Values for 〈Δ E down 〉, the average downward energy transferred from the reactant to the bath gas upon collision, have been obtained for highly vibrationally excited undeuterated and per‐deuterated isopropyl bromide with the bath gases Ne, Xe, C 2 H 4 , and C 2 D 4 , at ca. 870 K. The technique of pressure‐dependent very low‐pressure pyrolysis (VLPP) was used to obtain the data. For C 3 H 7 Br, the 〈Δ E down 〉 values (cm −1 ) are 490 (Ne), 540 (Xe), 820 (C 2 H 4 ), and 740 (C 2 D 4 ), and for C 3 D 7 Br, 440 (Ne), 570 (Xe), 730 (C 2 H 4 ), and 810 (C 2 D 4 ). The uncertainties in these values are ca. ±10%. The 〈Δ E down 〉 values for the inert bath gases Ne and Xe show excellent agreement with the theoretical predictions of the semi‐empirical biased random walk model for monatomic/substrate collisional energy exchange [ J. Chem. Phys. , 80 , 5501 (1984)]. The relative effects of deuteration of the reactant molecule on 〈Δ E down 〉 also compare favorably with the predictions of this theoretical model. Extrapolated high‐pressure rate coefficients (s −1 ) for the thermal decomposition of reactant are 10 13.6±0.3 exp(−200 ± 8 kJ mol −1 / RT ) for C 3 H 7 Br and 10 13.9±0.3 exp(−207 ± 8 kJ mol ±1 / RT ) for C 3 D 7 Br, which are consistent with previous studies and the expected isotope effect.