Theoretical Study on the Spectroscopic Properties and Photodissociation Mechanism of Dibromocarbene.

Detailed calculations on the electronic states of dibromocarbene (CBr2) herein are presented. First, the spectroscopic properties of the electronic states including geometry parameters, harmonic vibrational frequencies and transition energies of the lowest electronic states of the neutral radical were calculated in detail using the internally contracted multireference configuration interaction methods including Davidson correction (icMRCI+Q) with correlation consistent basis sets of aug-cc-pVXZ (X = T, Q, 5). Second, as CBr2 including two Br atoms, the Spin-Orbit Coupling (SOC) effect on the spectroscopic parameters and the one-dimensional cuts of the potential energy surface (PESs) of the lowest three states were studied. The barrier to linearity and dissociation of the singlet state were discussed. Third, the one-dimensional cuts along with the vertical transition energy (VTE), the oscillator strength, and so on of the electronic states related to the several lowest dissociation limits of CBr2 were calculated at the icMRCI+Q/aug-cc-pVTZ level. Based on the computed results of the electronic states of the radical, the photodissociation mechanism in the UV region were discussed in detail. The ab initio calculations are compared with the previous theoretical and experimental data and are in good agreement. The present work will provide a comprehensive understanding on the electronic structures and dissociation dynamics for the electronic states of the CBr2 radical.

An ab initio study on the electronic excited states and photodissociation mechanism of bromocarbene molecule.

We used the internally contracted explicitly correlated multireference configuration interaction (icMRCI-F12) method combined with Davidson correction to conduct a high-precision ab initio study of CHBr. The spin-orbit coupling (SOC) is incorporated into the calculation. The 21 spin-free states split into 53 spin-coupled states of CHBr. The vertical transition energies and oscillator strengths are obtained of these states. The SOC effect on the equilibrium structures and the harmonic vibrational frequencies of the ground state X1A', the lowest triplet state a3A'' and the first excited singlet state A1A'' is investigated. The results reveal a significant effect of the SOC on the bond angle and the frequency of the bending mode of a3A''. The potential energy curves of electronic states of CHBr as functions of the H-C-Br bond angle, C-H bond length, and C-Br bond length, respectively, are also investigated. Based on the calculated results, the interactions between electronic states and photodissociation mechanism involved in CHBr in the ultraviolet region are explored. Our theoretical studies will shed light on the complicated interactions and dynamics of the electronic states of bromocarbenes.

Theoretical Study on the Excited Electronic States of CHCl: Application to Photodissociation at 193 nm.

We present herein a high-level ab initio study on the electronic excited states of CHCl using the internally contracted multireference configuration interaction method including Davidson correction (icMRCI+Q). A total of 13 electronic states with energy of up to 7 eV have been investigated. The vertical transition energies, oscillator strengths, electron configurations, and transitions of the electronic states of CHCl have been calculated at the icMRCI+Q/aug-cc-pv(5+d)Z level. The potential energy curves of the electronic states have been studied along the H-C-Cl angle, the C-H bond length, and the C-Cl bond length, respectively. Our theoretical study has provided comprehensive information for understanding the interaction and the behavior of the electronic excited states of CHCl. In particular, the excited state involved in the 193 nm photodissociation as well as the corresponding dissociation dynamics have been discussed on the basis of our calculation results. The present study should shed more light on the photochemistry of CHCl in the ultraviolet region.

All-electron relativistic multireference configuration interaction investigation of fluoroiodo carbene.

We present herein the first all-electron relativistic internally contracted multireference configuration interaction with Davidson correction (icMRCI+Q) study on the low-lying states of fluoroiodo carbene, CFI, which contains the most electronegative element (fluorine) and the heavy halogen (iodine). The potential energy surface (PES) of the first excited singlet state (Ã(1)A″) of CFI was carefully examined along the C-I bond distance at the icMRCI+Q/ANO-RCC level, while the other two geometric parameters were optimized at every C-I bond length in contrast to fixing them at the equilibrium values. A reliable barrier height of the Ã(1)A″ state was determined to be 625 cm(-1) by our high-level icMRCI+Q calculations with large ANO-RCC basis set and with inclusion of the spin-orbit coupling, core-valence correlation, and zero-point-energy. Finally, the electronic states of CFI with vertical transition energy up to 6 eV were studied. The calculation presented here will provide more comprehensive results about the structure and behavior of electronic states of CFI radical.

Potential energy curves and lifetimes of low-lying excited electronic states of CSe studied by configuration interaction method.

In this work, we performed a high level ab initio study on the low-lying electronic states of CSe, utilizing MRCI+Q (the internally contracted multireference configuration interaction, and Davidson's correction) method with scalar relativistic and spin-orbit coupling effects taken into account. The potential energy curves of 18 Λ-S states associated with the lowest dissociation limit of CSe molecule, as well as those of 50 Ω states generated from the Λ-S states were computed. The spectroscopic parameters of bound states were evaluated, which agree well with existing theoretical and experimental results. With the aid of calculated spin-orbit matrix elements and the Λ-S compositional variation of the Ω states, the spin-orbit perturbations of low-lying states to the A(1)Π and a(3)Π states are analyzed. Finally, the transition dipole moments of A(1)Π, A'(1)Σ(+), a(3)Π0+, and a(3)Π1 to the ground X(1)Σ(+) state as well as the lifetimes of the four excited states were evaluated.

Ab initio MRCI+Q study on low-lying states of CS including spin-orbit coupling.

Carbon monosulfide (CS), which plays an important role in a variety of research fields, has long received considerable interest. Due to its transient nature and large state density, the electronic states of CS have not been well understood, especially the interactions between different states. In this paper, we performed a detail ab initio study on the low-lying electronic states of CS by means of the internally contracted multireference configuration interaction method (including Davidson correction) with scalar relativistic correction using the Douglas-Kroll-Hess Hamiltonian. We focused on the spin-orbit coupling of the states via the state interaction method with the full Breit-Pauli Hamiltonian. The potential energy curves (PECs) of 18 Λ-S states correlated with the lowest dissociation limit of the CS molecule were calculated, as well as those of 50 Ω states generated from the Λ-S states. The spectroscopic constants of the bound states were obtained, which are in good agreement with previous available experimental and theoretical results. The state perturbations of the a(3)Π and A(1)Π states with other low-lying electronic states are discussed in detail, based on the calculated spin-orbit matrix as well as the PECs of the Ω states. Avoided crossing in the states of CS was indicated when spin-orbit coupling was taken into account. Finally, the allowed transition dipole moments as well as the lifetimes of the five lowest vibrational states of the A(1)Π1, A'(1)Σ(+)0(+) and a(3)Πi states were obtained.

An ab initio investigation of fluorobromo carbene.

Fluorobromo carbene, an important halogenated carbene in the stratospheric ozone depletion, has long been received considerable interest. However, the energy, structure, and dynamics of even the lowest excited states have not been well understood. In this paper, we performed a detail ab initio study on CFBr using complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) method. We investigated the effect of basis set on the CASPT2 results of the ground X(1)A' state and the first excited singlet A(1)A" state. The potential energy surface (PES) of the A(1)A" state along C-Br bond distance was carefully examined at CASPT2/cc-pV5Z level, by optimizing C-F bond and F-C-Br angle at every C-Br bond length in contrast to fix them at the equilibrium values. On the basis of the PES, a reliable barrier height of the A(1)A" state was obtained from CASPT2 and MRCI+Q calculations with different basis sets, considering the scalar relativistic effect, spin-orbit coupling, and core-valence correlation. Finally, we carried out the first theoretical study on higher excited state with energy up to 7 eV. The present calculated results were compared with previous experimental and theoretical results where available. Our results will add some understanding and shed more light on the structure and dynamics of electronic states of CFBr radical.