Theoretical study of photodetachment processes of anionic boron cluster. III. B7−

Photoionization of aziridine: Nonadiabatic dynamics of the first six low-lying electronic states of the aziridine radical cation

In this article, the theoretical photoionization spectroscopy of the aziridine (C2H5N) molecule is investigated. To start with, we have optimized the geometry of this molecule at the neutral electronic ground state at the density functional theory/augmented correlation-consistent polarized valence triple zeta level of theory using the G09 program. The electronic structure calculations were restricted to the first six low-lying electronic states in order to account for the experimental photoelectron spectrum of the C2H5N molecule. The first six low-lying electronic states (X̃2A', Ã2A', B̃2A″, C̃2A″, D̃2A', and Ẽ2A') of the potential energy surfaces (PESs) are calculated by both equation of motion-ionization potential-coupled cluster singles and doubles and multi-configuration quasi-degenerate perturbation theory ab initio quantum chemistry methods along the dimensionless normal displacement coordinates in which multiple conical intersections were established among the considered electronic states. A (6 × 6) model vibronic Hamiltonian is constructed on a diabatic electronic basis, using the symmetry selection rules and Taylor series expansion. The Cs symmetry point group of the aziridine molecule leads to electronic states symmetry of either A' or A″, and these states are close in energy, due to which the same symmetry electronic states avoid each other. To get a smooth diabatic PES, a fourfold diabatization scheme is used, which is implemented in the General Atomic and Molecular Electronic Structure Systems suite of programs. All the parameters used in the diabatic vibronic coupling model Hamiltonian are calculated in terms of the normal modes of vibrational coordinates. Finally, the vibronic model Hamiltonian constructed for the coupled six electronic states is used to solve both time-independent and time-dependent Schrödinger equations using the multi-configuration time-dependent Hartree program module to obtain the dynamical observables. The theoretical vibronic band structure is found to be in good accord with the available experimental results.

Resolving the Experimental Photoelectron Spectra of CAl3Si. J Phys Chem A 2024;128:355-369. [PMID: 38189257 DOI: 10.1021/acs.jpca.3c06295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The experimental photoelectron spectra concerning the six electronic states of CAl3Si- are resolved through electronic structure calculations and quantum nuclear dynamics in this study. It incorporates a model diabatic Hamiltonian to evaluate the coupling parameters and fit the potential energy curves (PECs). The analysis of these PECs showed us that there are sufficient nonadiabatic effects in the photoelectron spectra through the presence of various conical intersections. Poisson intensity distributions (PIDs) and the wave packet density plots are utilized for assigning the fundamental and first overtone excitations. The nuclear dynamics study is accomplished by employing time-dependent (TD) and time-independent (TI) quantum chemistry methods. Ultimately, our theoretical results concurred well with the experimental findings exhibiting vibronic coupling amidst the nearly positioned electronic states.

A theoretical study of vibronic coupling in the photoelectron spectra of Al6N. Phys Chem Chem Phys 2023;25:12990-13003. [PMID: 37165932 DOI: 10.1039/d3cp00836c]

This work emphasizes the appearance of non-adiabatic effects in the photoelectron spectra of Al₆N^-. It includes ab initio electronic structure calculations obtained on the first seven low-lying electronic states of Al₆N^- and a nuclear dynamics study utilizing time-dependent and time-independent quantum chemistry approaches. A model vibronic Hamiltonian is constructed in a diabatic electronic representation to estimate the coupling parameters corresponding to the fifteen vibrational modes of Al₆N^-. Theoretical spectral bands are achieved by employing the vibronic coupling theory followed by reduced dimensional calculations to understand the role of individual vibrational modes in the overall photoelectron spectra. Finally, the theoretically obtained photodetachment spectra show good agreement with the experimental spectra revealing vibronic coupling among the closely spaced spectral bands.

Unraveling the Photoelectron Spectrum of 1-Phospha-2,3,4-triazolate Anion, HCPN3-, A Theoretical Approach

The first five low-lying electronic states of HCPN₃ are probed through extensive ab initio electronic structure and quantum dynamics studies to reproduce the 193 nm photoelectron spectrum. Vibronic Hamiltonian is constructed and availed for time-dependent (TD) and time-independent (TI) quantum dynamical studies. The presence of numerous conical intersections (CIs) and crossings among electronic states yielded interesting nonadiabatic effects in the photoelectron bands of the overall spectrum. Moreover, the theoretical bands corresponding to five electronic states have reproduced all three experimental spectral bands. Among these, the first two bands originated due to a combination of four electronic states as predicted by previous studies. The third band corresponds to the fifth electronic state. The results calculated via TD and TI approaches exhibited satisfying agreement with the experimental results.

Understanding of the Photodetachment Spectrum of Anionic Mixed Carbon-Boron Cluster C3B5- Following Adiabatic and Nonadiabatic Quantum Chemistry Approaches

The presence of nonadiabaticity in the photodetachment bands of the anionic mixed carbon-boron cluster C₃B₅^- has been realized through ab initio electronic structure calculations and detailed analyses of quantum dynamics study on top of those electronic structures. In the course of our study, we traverse extensive first principles electronic structure calculations to compute potential energy curves and to trace the energetic locations for the conical intersections in the multidimensional surfaces. All the ab initio calculations are performed on the four low-lying electronic states of the C₃B₅ cluster, while quantum nuclear dynamics are pursued on those electronic states by applying both time-dependent and time-independent quantum chemistry frameworks. In particular, we rely on the diabatic electronic representation to construct the molecular Hamiltonian. Altogether, the simulated theoretical spectra offer exceptional agreement with the experimental attainments.

An unbiased confirmation of the participating isomers of C2B5- in the formation of its photo-detachment spectra: a theoretical study

The primary goal of the present article is to provide an unbiased structural confirmation of C2B5-, relying on its available experimental photo-detachment spectra. The study is performed from scratch by optimizing the lowest energy isomers of C2B5- and later, suitable molecular vibronic Hamiltonians are constructed by analyzing the normal modes of these optimized isomers. The Hamiltonians' parameters are evaluated from the fits of the calculated ab initio single point energies using a state of the art multireference configuration (MRCI) level of theory employing a correlation consistent polarized triple zeta (cc-pVTZ) basis set. The state-averaged variant of the MRCI level of theory is also applied to deal with the highly interactive electronic states of both of the isomers. A detailed analysis of the potential energy curves along the totally symmetric vibrational modes is performed to understand the energy modulation between the different electronic states and also to find the energetic locations of the conical intersections. The introduction of the non-symmetric vibrational modes in the Hamiltonians help to understand the impact of non-adiabaticity during energy modulation in the coupled surfaces. Later, both adiabatic and non-adiabatic nuclear dynamics are performed on the electronic states of both of the isomers using the constructed reduced and full-dimensional Hamiltonians. The results of the adiabatic dynamics are used to assign the positions of the simulated photo-detachment bands, while the non-adiabatic dynamics improve the shape of those bands. Finally, we compare our theoretical findings with the available experimental photo-detachment spectra of C2B5- to provide an unbiased structural confirmation of the participating isomers of C2B5- in its photo-detachment spectra.

Electronic structure and photoelectron spectra of Bnwith n = 26–29: an overview of structural characteristics and growth mechanism of boron clusters

In this report, the electronic structure and photoelectron spectra of boron clusters B_26–29were theoretically investigated and an overview of the growth mechanism of boron clusters was shown.