Study of halogen–carbon dioxide clusters and the fluoroformyloxyl radical by photodetachment of X−(CO2) (X=I,Cl,Br) and FCO−2

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Abstract
Photoelectron spectra have been measured for the anions X−(CO2), with X=I, Br, Cl, and F. The vibrationally resolved spectra show that I−(CO2), Br−(CO2), and Cl−(CO2) are primarily electrostatically bound clusters, although the charge‐quadrupoleinteraction is strong enough to distort the CO2 molecule by as much as 10° [in Cl−(CO2)]. Ab initio calculations and electrostatic models are used to describe the geometry and bonding of these clusters. The photoelectron spectrum of FCO− 2 is qualitatively different and shows transitions to both the X̃ 2 B 2 ground and the à 2 A 2 first excited electronic states of the covalently bound FCO2 radical. The previously unobserved à 2 A 2 state is measured to lie 0.579 eV above the ground state. Vibrational frequencies are assigned with the assistance of ab initio calculations. The FCO2 heat of formation is determined to be Δ fH0 298(FCO2)=−85.2±2.8 kcal/mol. While both FCO− 2 and FCO2 are more strongly bound than the other halide–CO2 clusters, the C–F bonds are very weak relative to C–F bonds found in other halocarbon compounds.