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Enhancement of the bimolecular reaction of hydrogen iodide by vibrational excitation
Author(s) -
Horiguchi Hiroyuki,
Tsuchiya Soji
Publication year - 1981
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.550131008
Subject(s) - chemistry , excited state , excitation , atomic physics , torr , hydrogen , activation energy , laser , irradiation , reaction rate , vibrational temperature , reaction rate constant , hydrogen iodide , analytical chemistry (journal) , photochemistry , kinetics , thermodynamics , biochemistry , physics , organic chemistry , optics , quantum mechanics , chromatography , nuclear physics , electrical engineering , engineering , catalysis
The bimolecular reaction of HI in CO 2 , which was excited vibrationally by irradiation of a continuous‐wave CO 2 laser light, was investigated in the temperature range of 721–980 K. An enhancement of the reaction rate by a factor of about 2.5 was observed in the 1:1 HICO 2 mixture in comparison with the rate in pure HI when both sample gases were irradiated by a CO 2 laser (50 W) at 1 torr. However, in the HI‐SF 6 mixtures the decomposition rate of HI was not accelerated by irradiation of the CO 2 laser. Thus the enhancement is attributed to vibrational excitation of HI through collisional energy transfers from laser‐excited CO 2 (00°1). At lower total pressures or at lower partial pressures of HI in HI‐CO 2 mixtures the enhancement was more significant because of inefficient vibrational deactivation of excited HI. A model calculation gave the result in agreement with the experimental one if the effective activation energy is assumed as E a † = E a ‐ α E vib , where E a is the activation energy for the thermal reaction, E vib is the vibrational energy of two colliding HI molecules, and α is estimated to be about 0.7. This means that a part of the vibrational energy of reacting HI is employed to reduce the activation energy for the translational or rotational degree of freedom.