Insights into the Photoelectron Spectroscopy of Chlorofluoroethenes Studied by Density-Functional and Coupled-Cluster Theories

Abstract

The first two ionic states of chlorofluoroethenes were studied by using both time-independent and time-dependent density-functional theories. We calculated the equilibrium geometries and harmonic vibrational frequencies of 1,1-, cis-, and trans-C2H2FCl and their cations by using the B3LYP and B3PW91 functionals together with the cc-pVTZ and aug-cc-pVTZ basis sets. Franck-Condon factors were computed by the method developed in our group, in which the Duschinsky effect was treated explicitly. A new technique, named alignment transformation, followed by Euler transformations was developed to achieve the Eckart conditions. The adiabatic ionization energies were calculated by the CCSD(T) method extrapolated to the complete basis set limit. Insights into the simulated photoelectron spectra of C2H2FCl indicate that the resolutions of recent threshold photoelectron experiments are not high enough to detect individual transitions. The high-resolution photoelectron spectra of C2H2FCl are predicted for future reference. The computed adiabatic ionization energies of the three isomers of C2H2FCl are in accord with the experiments with the absolute deviations ranging from 0.004 to 0.021 eV. We suggest that the agreement between experimental and theoretical spectra should be a key criterion to judge whether a spectral assignment is reasonable.

Study of the Vibrational Spectra and Absorption Cross Sections of 1-Chloro-1-fluoroethene by a Joint Experimental and Ab Initio Approach

“…55 By using synchrotron radiation, the photoabsorption spectrum between 5 and 15 eV was recently analyzed, 56,57 and the valence/Rydberg transition region centered around 7 eV was investigated, thus extending the previous available data. 58 In addition, its adiabatic ionization energy has been recently 59 computed by CBS method, and its first two ionic states have been studied by employing both time-dependent and timeindependent density functional theories.…”

A theoretical study of the photoelectron spectra of dichloroketene with accurate computation of ionization energies via complete basis set limit extrapolation

“…The first formula was developed by Peterson et al (Equation ) where E ( x ) is the energy for x = 2, 3, 4, 5 (corresponding to X = D, T, Q, 5), E CBS is the CBS limit energy, and A and B are adjusting parameters. According to our experience and assessments in the literature, Equation is very accurate. An extensive review regarding the performance of different CBS formulas was provided by Feller et al However, we searched for new CBS formulas that could perform equally well or even better than Equation .…”

“…The details of the approach of spectral simulation developed by our group have been described elsewhere, and are only briefly provided here. First, the equilibrium geometries and harmonic vibrational frequencies of the neutral and five cationic states of dichloroketene were obtained using the B3LYP, PBE0, and M06 functionals of the density functional theory (DFT) associated with the aug‐cc‐pVTZ (AVTZ hereafter) basis set .…”

“…The full width at half maximum (FWHM) of each peak was set to 10 cm −1 for simulating the high‐resolution spectrum but was adjusted for comparing the simulated spectrum with the experiment. Although the equilibrium geometries and vibrational normal modes were obtained using the Gaussian 09 package, the FCF and PES were computed by adopting the programmes written by our group …”

“…In the past decade, we have developed various approaches for computing Franck‐Condon integrals (FCIs) of harmonic oscillators (HOs), and the most complete solution refers to our publication in 2013 in which a general formula of FCI for HO is obtained by taking account of the Duschinsky effect, which describes the mixing of normal modes between two electronic states due to geometrical change. We have applied our approaches to investigate the photoelectron spectrum (PES) of molecules and found that the theoretical spectrum is powerful for interpreting the experimental observation.…”