I2 molecular elimination in single-photon dissociation of CH2I2 at 248 nm by using cavity ring-down absorption spectroscopy

Abstract

Following single-photon dissociation of CH(2)I(2) at 248 nm, I(2) molecular elimination is detected by using cavity ring-down absorption spectroscopy. The technique comprises two laser beams propagating in a perpendicular configuration, in which a tunable laser beam along the axis of the ring-down cell probes the I(2) fragment in the B (3)Π(ou)(+) - X (1)Σ(g)(+) transition. The nascent vibrational populations for v = 0, 1, and 2 levels are obtained with a population ratio of 1:(0.65 ± 0.10):(0.30 ± 0.05), corresponding to a Boltzmann-like vibrational temperature of 544 ± 73 K. The quantum yield of the ground state I(2) elimination reaction is determined to be 0.0040 ± 0.0025. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state CH(2)I(2) via internal conversion, followed by asynchronous three-center dissociation. A positive temperature effect supports the proposed mechanism.

Studies via Near-Infrared Cavity Ringdown Spectroscopy and Electronic Structure Calculations of the Products of the Photolysis of Dihalomethane/N2/O2Mixtures

“…We found 2.0 mJ/pulse of 248 nm light (2.5 × 10 15 photons) is absorbed by the CH 2 I 2 precursor. CH 2 I 2 has a quantum yield of 1, yielding 2.5 × 10 15 CH 2 I radicals. Assuming all CH 2 I radicals produce methylene peroxy (as Su et al did).…”

BrCl+ elimination from Coulomb explosion of 1,2-bromochloroethane induced by intense femtosecond laser fields

“…This conclusion of 1,2-BCE is in agreement with the previous literature on polyhalogenalkanes that halogen product pathway is regarded as the primary fragmentation pathway for polyhaloalkanes. [1][2][3][4][5][6][7][8][9][10][11][12] The aim of the present work has been to explore the mechanism on unimolecular ion elimination of BrCl + , so we would concentrate on BrCl + and its partner C 2 H 4 + in the sections below.…”

“…The photodissociation of polyhalogenalkanes induced by intense laser elds has been extensively studied and is the subject of recent reviews. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Two major reactions are possible for dissociation of polyhalogenalkanes: the halogen atom release reaction channel and the halogen molecular elimination reaction channel. Thus far, most studies have been focused on the halogen atomic product channel, and the halogen molecular elimination channel as a research topic has received less attention in earlier papers.…”

“…9,12 Many authors have tried to explain the detachment mechanism of halogen molecular fragments from polyhalogenalkanes. [4][5][6][7][8][9][10][11][12][13][14] Lin and co-workers 4-7 investigated photodissocation of CH 2 Br 2 , C 2 H 4 Br 2 , CH 2 I 2 , and CH 2 BrI to molecular products of Br 2 , I 2 , and BrI by cavity ringdown absorption spectroscopy at 248 nm. Their theoretical calculations on potential energy surface of the polyhaloalkanes revealed that these halogen molecular dissociation channels were anticipated to proceed via an asynchronous concerted mechanism.…”

Phase-shift Cavity Ring Down Spectroscopy Set-up for NO2 Sensing : Design and Fabrication

“…The PS-CRDS is one of the categories of cavity ring down laser spectroscopy (CRDS) in which the phase difference between input and the output intensity signal is measured. This technique is extremely sensitive due to high signal-to-noise ratio and can be used to study the weak absorption features, pre-dissociation stages, and overtones in the molecular species 13,14 . Several experiments have been reported in the area of detecting and studying the thermodynamics, chemical kinetics, and spectroscopy of the various toxic gases [15][16][17] .…”