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

Abstract

We calculated the equilibrium geometries and harmonic vibrational frequencies of the ground state and five cationic states of dichloroketene using (TD‐)B3LYP, PBE0, and M06/M06‐2X approaches. The photoelectron spectra of dichloroketene were simulated by computing Franck‐Condon factors. The ionization energies were computed using the CCSD(T) approach with extrapolation to the complete basis set (CBS) limit. We propose two new CBS energy formulas (E = ECBS + Aexp(‐x) + B/(x−1) n, n = 2 or 3) and compare the performance of different CBS approaches. A new ionic state of dichloroketene belonging to the Cs point group is reported. This state is identified as the first excited state of Cl2CCO+ having a double‐well potential‐energy curve along the CCO bending mode with a barrier height of 1.335 eV. The simulated photoelectron spectra are in agreement with the experiment. The vertical ionization energies calculated via spectral simulation are more accurate compared with those obtained at the ground‐state structure. Among the CBS formulas used, the proposed ansatz with n = 2 performs best, with a mean absolute error of 0.021 and 0.012 eV for the adiabatic and vertical ionization energies, respectively.

Theoretical Study of the Negative Ion Photoelectron Spectrum of Cyclooctatetraene via Computation of Franck–Condon Factors

“…In the above equations, eq is developed by Peterson et al, eq by Feller, , eq by Helgaker et al., and eq by Martin Equations and were recently proposed by our group for calculating the ionization energies of dichloroketene . Compared with the experimental ionization energies of dichloroketene, eq provides the smallest mean absolute error, followed by eqs and , which indicates that eqs and proposed by our group have potential to be the CBS formulas with high accuracy.…”

“…37 Equations 2 and 3 were recently proposed by our group for calculating the ionization energies of dichloroketene. 30 Compared with the experimental ionization energies of dichloroketene, eq 2 provides the smallest mean absolute error, followed by eqs 1 and 3, which indicates that eqs 2 and 3 proposed by our group have potential to be the CBS formulas with high accuracy. In this study, we compare the performance of the AEA computed by eqs 1−6 to examine whether eqs 2 and 3 are still valid.…”

“…In addition to predicting the PES of COT – , we also computed the adiabatic electron affinity (AEA) of COT with the complete basis set (CBS) limit method. Two new formulas for calculating CBS energies have been recently proposed by our group, and their accuracy for predicting the ionization energies of dichloroketene is competitive with four other popular formulas . To check the validity of our CBS formulas, we applied them to calculate the AEA of COT and compared the result with the experimental value.…”

Reassignment of the Photoelectron Spectrum of Methylketene Using a Hybrid Model of Harmonic and Anharmonic Oscillators to Compute Franck–Condon Factors

“…At the B3LYP/AVTZ optimized geometries of MK and MK + , single-point energies were calculated using the CCSD­(T) approach in conjunction with the AVXZ (X = D, T, Q, 5) basis sets. The CCSD­(T) energies were extrapolated to the CBS limit using six different formulas, i.e., ,− where A and B are adjusting parameters, E CBS is the CBS energy, and x = 2, 3, 4, 5 corresponding to the AVXZ (X = D, T, Q, 5) basis sets, respectively. We used six different CBS formulas because eqs and were developed by our group, and we want to compare the performance of our formulas with the other four in predicting molecular properties involving energies.…”

“…In the past decade, we have developed some approaches for computing FCFs of harmonic oscillators. ,− The Duschinsky effect has been taken into account in our model for polyatomic molecules . Our harmonic model for computing FCFs has been successfully applied to the studies of the PES of some molecules. − However, the excitation energies computed by the harmonic model are usually larger than the experimental values. Accordingly, we constructed a hybrid model of harmonic and anharmonic oscillators to compute the FCFs and simulate the vibronic spectra of the molecules in this study.…”