Assignment of the First Photoelectron Band of CH3CHBr(X2A) Using Ab-initio and Density Functional Theory (DFT) Computational Calculations

Abstract

HeI photoelectron spectra have been recorded for the reaction of atomic fluorine with ethyl bromide at different reaction times. A structured band associated with a short-lived primary reaction product has been recorded at a mixing distance of 12 mm above the photon beam. The adiabatic and vertical ionization energies of this band was measured as 7.78 ± 0.01 and 8.05 ± 0.01 eV, respectively . The average vibrational separation of 700 ± 30 cm−1 was observed in this band. Vertical ionization energies were computed in this work for CH3CHBr(X2A) and CH2CH2Br(X2A) via ΔSCF, ΔMP2 (full) and Δ(B3LYP) levels of theory using different basis sets. Mulliken population analysis and force constant calculations have also been carried out for CH3CHBr(X2A) and CH2CH2Br(X2A) and their singlet cationic states. Comparison between the experimental vertical ionization energies and the corresponding values computed for CH3CHBr (X2A) and CH2CH2Br(X2A) at different levels of theory led to the assignment of the observed first photoelectron band to the ionization of CH3CHBr(X2A). The observed vibrational structure was assigned to the excitation of C–Br stretching mode in CH3CHBr+ (X1A).