Laser-Induced Fluorescence of the CHClCHO Radical and Reaction of Oxygen Atoms with Halogenated Ethylenes

Abstract

A new laser-induced fluorescence spectrum has been observed in the region 320−360 nm. Since this spectrum is observed when reacting oxygen atoms with chlorinated ethylenes such as CH2CHCl, CH2CCl2, CHClCHCl, and CHClCHF and also when chlorine atoms react with chloroacetaldehyde, the fluorescing molecules are identified as cis- and trans-2 chlorovinoxy radicals (cis- and trans-CHClCHO). From an analysis of the laser-induced single vibronic level fluorescence, some of the vibrational frequencies can be assigned for the ground electronic state (X̃ 2A‘ ‘): ν3(CO str) = 1567, ν4(CH rock.) = 1380, ν5(CH rock.) = 1309, ν6(CC str) = 1060, ν7(CCl str) = 820, ν8(CCO bend.) = 677, and ν9(CCCl bend.) = 220 cm-1 for cis-CHClCHO; ν3 = 1581, ν4 = 1379, ν5 = 1267, ν6 = 1145, ν7 = 942, ν8 = 472, and ν9 = 324 cm-1 for trans-CHClCHO. Some of the vibrational frequencies for the excited B̃2A‘ ‘ state also are assigned. These vibrational assignments are supported by ab initio calculations. The calculated geometries of the cis- and trans-CHClCHO radicals are planar in the ground state and slightly nonplanar in the excited state. Radiative lifetimes of the excited cis- and trans-CHClCHO radicals are also reported. The experimental results showed that the C−C−O skeleton and spectroscopic character of the cis- and trans-CHClCHO are closer to those of CH2CHO than to those of CH2CFO. The mechanisms of the O + halogenated ethylene reactions are discussed.

Multireference Configuration Interaction Calculation of the B̃2A‘ ‘−X̃2A‘ ‘ Transition of Halogen- and Methyl-Substituted Vinoxy Radicals

“…Figure 5 shows rotational profiles of the 0-0 band of trans-CHClCHO radical in the fluorescence excitation spectrum after the reaction of CH 2 -CCl 2 + O( 3 P) at room temperature. 19 The spectrum of trans-CHClCHO shows that the 0-0 band at 29040 cm -1 and hot bands at 28993, 28947, and 28898 cm -1 have a tail on the lower wavenumber side. A simulated spectrum of the 0-0 band of trans-CHClCHO in Figure 5 shows an asymmetrical peak with a tail on the lower wavenumber side and its width at half height was about 60 cm -1 .…”

“…We have already shown in the case of unsubstituted and halogenated vinoxy radicals that CASSCF calculation provides excitation energies and vibrational frequencies that are helpful for assignment of vibronic peaks in fluorescence spectra. [18][19][20] However, discrepancies between calculated and observed excitation energies exceeded 0.1 eV in some cases and observed blue shift of excitation energies by increasing the number of substituted atoms were not correctly reproduced. 26 These results imply that dynamical correlation must be taken into account to obtain quantitatively accurate potential energy surfaces of the excited states.…”

Photodissociation spectroscopy and dynamics of the CH2CFO radical

“…2 Calculations of optimized geometries and vibrational frequencies for the X and B states of CH 2 CFO using the complete active space self-consistent field ͑CASSCF͒ method established that the observed band was the result of exciting the B state. 3 Spectral assignments, aided by measured dispersed fluorescence spectra, revealed excitation of the 3 ͑C-O stretch͒, 4 ͑CHH scissor͒, 5 ͑C-F stretch͒, 6 (CH 2 rock͒, 7 ͑C-C stretch͒, 8 ͑FCO bend͒, and 9 ͑CCO bend͒ modes of the B state. 1,6 The LIF study by Furubayashi et The heats of formation used to obtain the heats of reaction for channels ͑1͒-͑3͒, ͑5͒, and ͑6͒ are listed in Table I, while the heat of reaction for channel ͑4͒ is obtained from the theoretical work by Cao et al 7 The energy level diagram for CH 2 CFO and these product channels is presented in Fig.…”

Temperature dependences of the reactions of O(3P) atoms with selected chlorofluoroethenes between 298 and 359 K

“…and the small temperature dependences detected for the four chlorofluoroethenes suggest a general mechanism for the reactions consisting of and electrophilic addition of the O atom to the -electron system of the halogenated ethene to form an energy-rich complex (a triplet biradical) which may either collisionally stabilize or unimoleculary decompose to form the products [16]. Our results show that the variations of ln k with 1/T are linear for the four reactions studied, suggesting that the reactions proceed via a single elementary pathway over the temperature range of our study and, furthermore, that this channel is addition of O( 3 P) to the chlorofluoroethenes.…”