Dynamics of OH and OD radical reactions with HI and GeH4 as studied by infrared chemiluminescence of the H2O and HDO products

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Abstract
The infrared chemiluminescence of vibrationally excited H 2 O and HDO from the highly exothermic reactions of OH and OD radicals with HI and GeH 4 was observed in the 2200–5500 cm −1 range. The experiments utilized a fast-flow reactor with 0.3–1 Torr of Ar carrier gas at 300 K; the OH(OD) radicals were produced via the H(D)+NO 2 reaction and the H or D atoms were generated by a discharge in a H 2 (D 2 )/Ar mixture. The H 2 O and HOD vibrational distributions were determined by computer simulation of the emission spectra in the 2200–3900 cm −1 range. The total vibrational energy released to H 2 O and HOD molecules is, respectively, 〈f v 〉=0.36 and 0.41 from HI and 〈f v 〉=0.46 and 0.51 from GeH 4 . These values are significantly smaller than for the reactions of OH and OD with HBr, 〈f v 〉=0.61 and 0.65. The populations of the O–H stretching vibration of HOD and the collisionally coupled ν 1 and ν 3 stretching modes of H 2 O decrease with increasing vibrational energy. In contrast, the vibrational distribution from the HBr reaction is inverted. The bending mode distributions in all stretching states of H 2 O and HOD extend to the thermodynamic limit of each reaction. A surprisal analysis was made for H 2 O(HOD) distributions from the title reactions and compared with that for OH(OD)+HBr. The surprisal analysis tends to confirm that the dynamics for the HI and GeH 4 reactions differ from the HBr reaction. The HI reaction may proceed mainly via addition-migration, while the GeH 4 reaction may involve both direct abstraction and addition-migration. A rate constant for the OH+GeH 4 →H 2 O+GeH 3 reaction was evaluated by comparing the H 2 O emission intensities with that of the OH+HBr→H 2 O+Br reaction, k GeH 4 /k HBr =6.5±0.9 . Secondary kinetic-isotope effects, k OH /k OD =1.4±0.1 , 1.0±0.2, and 1.3±0.2, were determined for reactions of OH and OD with GeH 4 , HI, and HBr, respectively, by comparing the relative H 2 O and HOD emission intensities.