Theoretical Study on the Kinetic and Mechanism of H+HO2 Reaction

Abstract

The kinetics and mechanism of reaction of a hydroperoxyl radical (HO2) with a hydrogen atom on both singlet and triplet surfaces were studied by employing DFT, CCSD, and G3 methods along with the Aug-cc-pVTZ basis set. MC-SCF and CCD methods were used to explore potential energy surfaces. Major end products from different channels were H2O+O, H2+O2, and OH. Formation of chemically activated hydrogen peroxide HOOH was the most exothermic path in this system that dissociates to the ground state OH(2Π) radicals. Another energized transient species was water oxide H2OO, which has local minimum on the singlet potential-energy surface. The energized water oxide rapidly isomerized to hydrogen peroxide HOOH or dissociated to H2O + O(1D). Transition state theory and RRKM theory were used to calculate the rate constants for different channels.

Formation mechanisms of oxygen atoms in the O(D21) state from the 157nm photoirradiation of amorphous water ice at 90K

“…31,32 Reactions ͑11͒-͑14͒ are endothermic and barrierless processes. 42 The translational and internal energies of the OH radicals from ASW after prolonged 157 nm irradiation on ASW are in good accordance with those of the OH radicals from fresh H 2 O 2 on ASW as shown in Table II Figure 4 shows that the hot OH radicals that can produce O͑ 1 D͒ atom could be formed from reaction ͑10͒. The large available energy in reaction ͑10͒ could accelerate O͑ 1 D͒ formation.…”

WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H2, AT 10 K

“…Even though the dissociation occurs, OH radicals are expected to recombine, resulting in the recovery of H 2 O 2 (reaction (6)) and/or the formation of H 2 O (reaction (7)), as follows: Walch et al (1988); Sellevag et al (2008). b Mousavipour & Saheb (2007). c Koussa et al (2006).…”

“…where H 2 OO* and H 2 O..O denote short-lived intermediate species (Mousavipour & Saheb 2007). Reaction channel (8) as a whole is slightly exothermic by 10 kJ mol −1 , whereas the latter part of the reaction (H 2 OO* → H 2 O + O( 1 D)) is highly endothermic by 151 kJ mol −1 (Mousavipour & Saheb 2007), indicating that reaction channel (8) would not go to completion if the intermediate H 2 OO* dissipated the excess energy to a cold surface.…”

“…Reaction channel (8) as a whole is slightly exothermic by 10 kJ mol −1 , whereas the latter part of the reaction (H 2 OO* → H 2 O + O( 1 D)) is highly endothermic by 151 kJ mol −1 (Mousavipour & Saheb 2007), indicating that reaction channel (8) would not go to completion if the intermediate H 2 OO* dissipated the excess energy to a cold surface. Reaction (9) has a huge barrier of about 9300 K, implying that the reaction proceeds only with difficulty, even with tunneling under astrophysically relevant conditions.…”

Role of OH radicals in the formation of oxygen molecules following vacuum ultraviolet photodissociation of amorphous solid water

“…[50][51][52] Our previous studies showed no contribution of HO 2 photoproducts on ASW to production of OH and O͑ 1 D and 3 P͒ following 157 nm photolysis of ASW, suggesting that the amount of HO 2 photoproducts on the ice surface was negligible at 90 K. Therefore, the O 2 formation following reactions of HO 2 +H or HO 2 + OH are considered to be unlikely sources for the observed O 2 ejection from the ASW surface in the present experiments. 3,53,54 Theoretical and experimental studies reported that the probabilities for the photodissociation processes of HO 2 to H+O 2 fragments were estimated to be small, since this photoprocesses are prohibited by potential barriers. 52 3 P͒ would react with OH much more frequently than they encounter another O͑ 3 P͒ to produce O 2 since concentration of primary product OH on ASW is much higher than that of O͑ 3 P͒ formed via secondary reaction on ASW.…”