Computation of Franck–Condon factors for many-atom systems: simulated photoelectron spectra of formic acid isotopologues

Abstract

Abstract Simulated photoelectron spectra of the four formic acid isotopologues HCOOH, HCOOD, DCOOH and DCOOD are reported. The simulations are based on computed multidimensional harmonic Franck–Condon factors (FCFs) for transitions from the ground state of the neutral molecule to the two lowest electronic states of the cation. The geometrical parameters and force constants used in the Franck–Condon analysis have been obtained at the B3LYP/6-311+G(3df,2p) level of theory. The results are compared with well-resolved experimental spectra, and good agreement between simulated and experimental spectra is found, in particular for the first PES band. Using the computed FCFs, the vibrational fine structure of the first two bands of the experimental spectra is analyzed, and vibrational frequencies for the two cationic states are extracted from the experimental data.