Construction of Beyond Born–Oppenheimer-Based Diabatic Surfaces of o-C₆H₄F2+ Radical Cation: Calculation of Photoelectron and Mass-Analyzed Threshold Ionization Spectra

Theoretically “exact” and numerically “accurate” Beyond Born–Oppenheimer (BBO)-based diabatic Hamiltonian for an aromatic radical cation, namely, o- (Formula presented.) H (Formula presented.) F (Formula presented.), is constructed theoretically for the first time, where the low-lying five electronic states ((Formula presented.), (Formula presented.), (Formula presented.), (Formula presented.), and (Formula presented.)) are nonadiabatically coupled with each other, exhibiting conical intersections (CIs)/seams due to accidental Jahn–Teller (JT) couplings as well as depicting pseudo-Jahn–Teller interactions. Once the diabatic PESs and couplings are constructed, those are used to execute multistate multimode nuclear dynamics for generating photoelectron (PE) and mass-analyzed threshold ionization spectra of the neutral analog. The calculated PE spectra for (Formula presented.), (Formula presented.), (Formula presented.), (Formula presented.) and (Formula presented.) states originated from the BBO-based diabatic Hamiltonian in conjunction with time-dependent discrete variable representation (TDDVR) dynamics show peak-by-peak correspondence with the experimental spectral bands as well as with other theoretical findings.