Enhancement of the bimolecular reaction of hydrogen iodide by vibrational excitation

Abstract

The himolecular reaction of HI in CO2, which was excited vibrationally by irradiation of a continuous-wave CO2 laser light, was investigated in the temperature range of K. An enhancement of the reaction rate by a factor of about 2.5 was observed in the 1:l HI-CO2 mixture in comparison with the rate in pure HI when both sample gases were irradiated by a CO2 laser (50 W) a t 1 torr. However, in the HI-SFe mixtures the decomposition rate of HI was not accelerated by irradiation of the C02 laser. Thus the enhancement is attributed to vibrational excitation of HI through collisional energy transfers from laser-excited CO2 (OOol).At lower total pressures or a t lower partial pressures of HI in HILC02 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 EA = E, -(~E,ib, where E, is the activation energy for the thermal reaction, E v i b is the vibrational energy of two colliding HI molecules, and (Y is estimated to he ahout 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.

Laser-induced addition of hydrogen fluoride to unsaturated molecules: the HF + CH2CF2 system

“…Indirect evidence for vibrational enhancement for a molecule/molecule reaction came from the results of Horiguchi and Tsuchiya (32), who irradiated HI and HI/C02 mixtures with a C 0 2 laser, and found an increased rate for the reaction when C 0 2 was present. This was said to be due to the nearresonant energy transfer from the excited C02 to the HI, followed by reaction between HI(v = 1) and HI(v = 0).…”