A study of the radical-radical reaction dynamics of O(P3)+t-C4H9→OH+iso-C4H8

Abstract

The radical-radical reaction dynamics of ground-state atomic oxygen [O(3P)] with t-butyl radicals (t-C4H9) in the gas phase were investigated using high-resolution laser spectroscopy in a crossed-beam configuration, together with ab initio theoretical calculations. The radical reactants, O(3P) and t-C4H9, were produced by the photodissociation of NO2 and the supersonic flash pyrolysis of the precursor, azo-t-butane, respectively. A new exothermic channel, O(3P)+t-C4H9 --> OH+iso-C4H8, was identified and the nascent rovibrational distributions of the OH (X 2Pi: upsilon" = 0,1,2) products were examined. The population analyses for the two spin-orbit states of F1(2Pi32) and F2(2Pi12) showed that the upsilon" = 0 level is described by a bimodal feature composed of low- and high-N" rotational components, whereas the upsilon" = 1 and 2 levels exhibit unimodal distributions. No noticeable spin-orbit or Lambda-doublet propensities were observed in any vibrational state. The partitioning ratio of the vibrational populations (Pupsilon") with respect to the low-N" components of the upsilon" = 0 level was estimated to be P0:P1:P2 = 1:1.17+/-0.24:1.40+/-0.11, indicating that the nascent internal distributions are highly excited. On the basis of the comparison of the experimental results with the statistical theory, the reaction mechanism at the molecular level can be described in terms of two competing dynamic pathways: the major, direct abstraction process leading to the inversion of the vibrational populations, and the minor, short-lived addition-complex process responsible for the hot rotational distributions. After considering the reaction exothermicity, the barrier height, and the number of intermediates along the addition reaction pathways on the lowest doublet potential energy surface, the formation of CH3COCH3(acetone)+CH3 was predicted to be dominant in the addition mechanism.

Reaction Dynamics of Phenyl Radicals in Extreme Environments: A Crossed Molecular Beam Study

“…In principle, both reactant beams can be prepared in well-defined quantum states before they cross at a specific collision energy under single collision conditions. The products can be monitored via spectroscopic detection schemes such as laser-induced fluorescence (LIF) 40 or Rydberg tagging, 41 via ion imaging probes, 42,43 or via a quadrupole mass spectrometric detector (QMS) with universal electron impact ionization or photoionization coupled to a mass spectrometric device. Here, the crossed molecular beam method with mass spectrometric detection presents the most versatile technique to study these elementary reactions thus permitting the elucidation of the chemical dynamics and, in the case of polyatomic reactions, the primary products.…”

A Theoretical Investigation of the Gas‐Phase Oxidation Reaction of the Saturated tert‐Butyl Radical

“…The nascent internal distributions of the OH products demonstrate substantial rovibrational excitations without any noticeable spin-orbit or L-doublet propensities. [17,18] The population analyses also reveal that the ground vibrational level (u" = 0) is composed of bimodal low-and high-rotational components, whereas the excited vibrational levels (u" = 1 and 2), which are significantly populated, exhibit unimodal distributions.…”

“…Recently, Choi and co-workers examined the exothermic OH channel (5) utilizing high-resolution, laser-induced fluorescence (LIF) spectroscopy in a crossed-beam configuration. [17,18] The nascent rovibrational distributions of the OH products obtained under single-collision conditions were found to be described in terms of two competing dynamic pathways: the major direct abstraction process leading to the inversion of the vibrational populations, and the minor short-lived addition-complex forming process responsible for the hot rotational distributions.…”

“…[11][12][13][14] In this work, we describe an ab initio investigation of the oxidation reaction of O( 3 P) with the saturated tert-butyl hydrocarbon radical (t-C 4 H 9 ), which was mainly motivated by our recent progress in a related gas-phase crossed-beam study. [15][16][17][18] The organic tert-butyl radical is a well-known important intermediate in combustion processes such as hydrocarbon cracking reactions. t-C 4 H 9 with C 3v symmetry is a relatively stable species as a result of the hyperconjugation resulting from the partial overlap of the sp 3 -s orbitals (CÀH bonds) with the empty p orbital of the central carbon.…”

“…[17,18] This reaction channel can be described in terms of two competing pathways: addition and abstraction. In comparison to the aforementioned addition pathway, the dominant process is clearly predicted to be the direct H-atom abstraction, as indicated in Figure 3.…”