The near ultraviolet spectrum of the FCO radical: Re-assignment of transitions and predissociation of the electronically excited state

Abstract

The electronic spectrum of the fluoroborane free radical. II. Analysis of laser-induced fluorescence and single vibronic level emission spectra Cavity ring-down spectra of the FCO radical, recorded over the wave number range 29 500-31 600 cm Ϫ1 reveal rotational structure of the electronically excited state for the first time. The spectra demonstrate the need for a complete re-assignment of the vibronic features: The rotationally resolved bands are successfully simulated as arising from c-type transitions from the ground X 2 AЈ state to the linear 2 AЉ component of the à 2 ⌸ state. The bands are attributed to two overlapping vibrational progressions: one progression involves excitation of the F-C-O bending mode (v 3 Ј), the other consists of a combination of v 3 Ј and one quantum of the C-F stretch (v 2 Ј). Sharp rotational structure is only observed for sub-bands with KЈϭ0; bands with KЈϾ0 are diffuse, indicating rapid, rotation induced predissociation. Band origins, rotational constants for the excited state, and spectral linewidths have been derived from the KЈϭ0 -KЉϭ1 sub-bands. All rotational lines are somewhat broadened and there is evidence of linewidths that increase with NЈ, and hence an additional rotation-induced predissociation mechanism. Vibrational frequencies and rotational constants are in excellent agreement with the predictions of ab initio calculations by Krossner et al., J. Chem. Phys. 101, 3973 ͑1994͒; 101, 3981 ͑1994͒. The à 2 ⌸(AЉ) -X 2 AЈ absorption shows characteristics of a transition between two Renner-Teller components and this interpretation is confirmed by careful examination of the electronic structure of the FCO ground state. Implications for assignments of absorption features at higher energy than the spectral region of the current study are discussed, and comparisons are drawn with the much studied electronic spectroscopy of both the HCO radical and the isoelectronic NO 2 .

4 Cavity ring-down and cavity enhanced spectroscopy using diode lasers

“…Because of its simplicity, ability to measure the absorption on an absolute scale, high sensitivity, and independence from pulse-to-pulse fluctuations of the laser (because of the analysis of time characteristics of the signal, rather than amplitudes), as well as its ready compatibility with small sample volumes or molecular beams, this technique has been widely used for various applications, spanning fundamental spectroscopy; [9][10][11][12][13][14][15][16][17][18] gas-phase circular dichroism measurements; 19 atmospheric photochemistry, 20,21 spectroscopy 22,23 and sensing; [24][25][26][27][28][29][30][31][32] environmental chemistry and pollution monitoring; [33][34][35][36] characterisation of temperatures, 37 electron densities 38 and chemical composition [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53]…”

Falloff Curves for the Recombination Reaction Cl + FC(O)O + M → FC(O)OCl + M

“…[4][5][6][7][8] In fact, certainly motivated by the assumed potential atmospheric importance of these species in cycles of depletion of stratospheric ozone, several time-resolved studies mostly performed by the flash photolysis technique have appeared since the nineties. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In addition, several spectroscopic [27][28][29][30][31][32][33][34] and ab initio quantum chemical studies dealing with the molecular properties of the FCO x (x ) 1-3) radicals have been reported. [22][23][24][25][26][27]29,32,34,[35][36][37][38][39][40][41][42][43]…”

“…In this context, the recombination reaction between chlorine atoms and fluoroformyloxyl radicals, FC(O)O forming fluoroformyl hypofluorite is considered in the present study. After the earlier studies on the kinetics and the reaction mechanisms of FC(O)O and the related FCO and FC(O)O 2 radicals reactions, no direct kinetic experiments related to these species appeared until the end of the last century. − In fact, certainly motivated by the assumed potential atmospheric importance of these species in cycles of depletion of stratospheric ozone, several time-resolved studies mostly performed by the flash photolysis technique have appeared since the nineties. − In addition, several spectroscopic − and ab initio quantum chemical studies dealing with the molecular properties of the FCO x ( x = 1−3) radicals have been reported. − ,,,,− …”

“…[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In addition, several spectroscopic [27][28][29][30][31][32][33][34] and ab initio quantum chemical studies dealing with the molecular properties of the FCO x (x ) 1-3) radicals have been reported. [22][23][24][25][26][27]29,32,34,[35][36][37][38][39][40][41][42][43][44][45] The appearance of FC(O)O radicals in the atmosphere follows FCO and FC(O)O 2 successive formation. The FCO radical is likely to be generated by photolysis of CF 2 O, and other carbonyl halides such as HFCO and CFClO, which are major degradation products of the photooxidation of fluorine containing halomethanes and haloethanes in the upper atmosphere.…”