Photoinitiated H- and D-atom reactions with N2O in the gas phase and in N2O–HI and N2O–DI complexes

A threedimensional quantum mechanical study of the NH+NO reactionsWe present a quasiclassical trajectory study of the NHϩNO reaction using a global potential energy surface that is capable of describing branching to the HϩN 2 O and OHϩN 2 products after initial formation of a HNNO intermediate complex. The surface is based on a many-body expansion wherein fragment potentials for the species N 2 H, HNO, and N 2 O are incorporated, using either previously developed potentials, or in the case of N 2 O, a newly developed potential. The three-body parts of these fragment potentials are damped in the four-body region to provide a zeroth order four-body surface, and then additional four-body terms and mapping transformations are applied to make the final four-body potential match the results of ab initio calculations for eight important HNNO stationary points ͑minima and saddle points͒ and for several reaction paths. In addition to this ''best fit'' surface ͑surface I͒, a second surface ͑surface II͒ is developed in which the ordering of the saddle points leading to formation of HϩN 2 O and OHϩN 2 is reversed, and the energy release during 1,3 hydrogen migration is modified so that the N-N stretch experiences smaller distortions from N 2 equilibrium during the reaction leading to OHϩN 2 . Quasiclassical trajectory results on surface I show generally good correspondence with experiment, with a branching fraction of 13Ϯ3% for the formation of OHϩN 2 at 300 K, and relatively low OH and N 2 vibration/rotation excitation. The results on surface II are similar with respect to both branching and energy partitioning, indicating relatively weak sensitivity of the results of key features of the surface.

Section: Introductionmentioning

confidence: 99%

A theoretical study of the NH+NO reaction

Bradley¹,

McCabe²,

Schatz³

et al. 1995

“…Böhmer et al observed an order of magnitude decrease in the ͓NH͔/͓OH͔ ratio when reaction was photoinitiated in clusters versus the gas phase ͑at the same wavelength͒. 5 It was considered unlikely that so large a change in the product channel branching ratio could be explained by just the squeezed atom effect acting in the binary cluster. 1 The squeezed atom effect increases the product center-of-mass translational energy at the expense of product internal energies in cluster versus gas phase reactions, and therefore it discriminates against the higher energy NHϩNO channel.…”

Section: Introductionmentioning

confidence: 95%

“…Marshall et al 3 measured and calculated thermal rates, k(T), for reactions ͑5͒-͑7͒. They were able to fit their experimental rates with the calculated ones over a broad temperature range and found the HNNO † intermediate to be the major pathway for temperatures р2000 K. Böhmer et al 5 subsequently recorded product state distributions for the reaction of 300 K N 2 O with fast hydrogen atoms produced by HI photolysis. They found significant N 2 vibrational excitation and attributed this to the participation of the HNNO † intermediate, in which case OH is formed by a 1,3-hydrogen shift mechanism.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast OH production in clusters containing N2O and HI

Ionov

Wittig

1997

Self Cite

The geometrical arrangement of reagents is an important factor influencing chemical reactions in condensed phases and molecular clusters. In the present study, OH buildup times have been recorded upon photolysis of (N 2 O) m (HI) n clusters in order to elucidate the role of the cluster environment on the reaction mechanism. The buildup times were measured for different molecular beam compositions ͑i.e., degrees of clustering͒. The buildup time changed from р100 fs at the lowest backing pressures ͑119 and 132 kPa͒ to 430 fs at 188 kPa. It is argued that at the lower backing pressures the OH derives primarily from binary N 2 O-HI complexes. However, regardless of the cluster species involved, the fast OH buildup at the lowest backing pressures suggests a dominant direct oxygen abstraction mechanism rather than reaction via a vibrationally excited intermediate such as HNNO † .

“…One is the occurrence of the so-called squeeze atom effect. 6,8 The idea of the ''squeeze atom effect'' is the following. The photolysis of H 2 S-O 2 leads at first simultaneous HS-H and H-O 2 repulsions that transmit forces to the heavier SH and O 2 species until the H atom becomes trapped on the HO 2 potential surface.…”

Section: Reaction Mechanism In the Half Reaction Conditionmentioning

confidence: 99%

“…The laser initiation of reaction from the ''geometry limited precursor'' potentially offers a unique opportunity to study the reaction under limited impact parameter as well as the limited orientation. [2][3][4][5][6][7][8][9][10] In this paper, an experimental study of the reaction of H atom with O 2 , H͑ 2 S ͒ϩO 2 ͑ X 3 ⌺ ͒→OH͑ X 2 ⌸,v,N,⍀,⌳ ͒ϩO͑ 3 P ͒ ͑1͒ by using the H 2 S-O 2 complex as a precursor, as well as the corresponding bulk reactions is presented.…”

Section: Introductionmentioning

confidence: 99%

Laser initiated half reaction study of H+O2→OH+O

Honma¹

1995

The HϩO 2 reaction system was studied under geometry limited half reaction conditions. The weakly bonded complex O 2 -H 2 S was formed by supersonic expansion, and reaction was initiated by 193 nm photoirradiation of the complex. Rotational, spin-orbit, and lambda doublet state distributions of product OH were determined by a laser-induced fluorescence ͑LIF͒ technique. The populations of the two spin-orbit states were observed to be statistical. The population of the ⌸͑AЈ͒ level was almost twice that of the ⌸͑AЉ͒ level, and the planar geometry was suggested for reaction path. These populations of the fine structures of OH were similar to those of OH formed under bimolecular reaction conditions. On the other hand, the rotational state distribution of OH from the half reaction has two components and the dominant one shows a very cold rotational distribution, in sharp contrast with that of the bimolecular reaction where rotation is highly excited. This cold rotational distribution could be partially explained by the absorption of a part of available energy by the internal motion of SH. However, the distribution with a peak at the lowest rotational level could not be explained by this effect, but ascribed to the exit interaction between SH and OH and/or the entrance channel specificity, i.e., the reaction occurs in limited impact parameters.