Bo-Zhen Chen

The 1 2A1, 1 2B2, and 1 2A2 states of the SO2+ ion studied using multiconfiguration second-order perturbation theory

The 1 (2)A(1), 1 (2)B(2), and 1 (2)A(2) electronic states of the SO(2) (+) ion have been studied using multiconfiguration second-order perturbation theory (CASPT2) and two contracted atomic natural orbital basis sets, S[6s4p3d1f]/O[5s3p2d1f] (ANO-L) and S[4s3p2d]/O[3s2p1d] (ANO-S), and the three states were considered to correspond to the observed X, B, and A states, respectively, in the previous experimental and theoretical studies. Based on the CASPT2/ANO-L adiabatic excitation energy calculations, the X, A, and B states of SO(2) (+) are assigned to 1 (2)A(1), 1 (2)B(2), and 1 (2)A(2), respectively, and our assignments of the A and B states are contrary to the previous assignments (A to (2)A(2) and B to (2)B(2)). The CASPT2/ANO-L energetic calculations also indicate that the 1 (2)A(1), 1 (2)B(2), and 1 (2)A(2) states are, respectively, the ground, first excited, and second excited states at the ground-state (1 (2)A(1)) geometry of the ion and at the geometry of the ground-state SO(2) molecule. Based on the CASPT2/ANO-L results for the geometries, we realize that the experimental geometries (determined by assuming the bond lengths to be the same as the neutral ground state of SO(2)) were not accurate. The CASPT2/ANO-S calculations for the potential energy curves as functions of the OSO angle confirm that the 1 (2)B(2) and 1 (2)A(2) states are the results of the Renner-Teller effect in the degenerate (2)Pi(g) state at the linear geometry, and it is clearly shown that the 1 (2)B(2) curve, as the lower component of the Renner splitting, lies below the 1 (2)A(2) curve. The UB3LYP/cc-pVTZ adiabatic excitation energy calculations support the assignments (A to (2)B(2) and B to (2)A(2)) based on the CASPT2/ANO-L calculations.

Hyperfine structure in HCS and related radicals: a theoretical study

Abstract The hyperfine structure of the HCS radical and the isovalent HCO, HSiS and HSiO radicals was studied using the B3LYP and MRSDCI methods. The B3LYP calculations predict an isotropic proton hyperfine coupling constant a (H) of 127.4–129.1 MHz for HCS, in excellent agreement with the experiment. The calculations confirm the experimental fact that the a (H) value of HCS is much smaller than the a (H) values of HCO, HSiS and HSiO, for which we present a simple explanation on the basis of the analysis of the spin densities on the heavy atoms.

The Bergman cyclizations of the enediyne and its N-substituted analogs using multiconfigurational second-order perturbation theory.

The Bergman cyclizations of the enediyne and its four N‐substituted analogs [(Z)‐pent‐2‐en‐4‐ynenitrile, 3‐azahex‐3‐en‐1,5‐diyne, malenotrile, and 3,4‐azahex‐3‐en‐1,5‐diyne] have been studied using the complete active space self‐consistent field and multiconfigurational second‐order perturbation theory methods in conjunction with the atomic natural orbital basis sets. The geometries and energies of the reactants, transition states, and products along both the S0 (the ground state) and T1 (the lowest‐lying triplet state) potential energy surfaces (PESs) were calculated. The calculated geometries are in good agreement with the available experimental data. The distance between two terminal carbons in enediyne, which was considered as an important parameter governing the Bergman cyclization, was predicted to be 4.319 Å, in agreement with the experimental value of 4.321 Å. Our calculations indicate that the replacements of the terminal C atom(s) or the middle C atom(s) in the CC bond by the N atom(s) increase or decrease the energy barrier values, respectively. There exist stable ring biradical products on the T1 PESs for the five reactions. However, on the S0 PESs the ring biradical products exist only for the reactions of enediyne, (Z)‐pent‐2‐en‐4‐ynenitrile, and 3‐azahex‐3‐en‐1,5‐diyne.

Dissociation of the OCS+ ion in low-lying electronic states studied using multiconfiguration second-order perturbation theory

Complete active space self-consistent-field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with atomic natural orbital basis sets were performed to investigate the S-loss direct dissociation of the 1 2Pi(X 2Pi), 2 2Pi(A 2Pi), 1 2Sigma+(B 2Sigma+), 1 4Sigma-, 1 2Sigma-, and 1 2Delta states of the OCS+ ion and the predissociations of the 1 2Pi, 2 2Pi, and 1 2Sigma+ states. Our calculations indicate that the S-loss dissociation products of the OCS(+) ion in the six states are the ground-state CO molecule plus the S+ ion in different electronic states. The CASPT2//CASSCF potential energy curves were calculated for the S-loss dissociation from the six states. The calculations indicate that the dissociation of the 1 4Sigma- state leads to the CO + S+ (4Su) products representing the first dissociation limit; the dissociations of the 1 2Pi, 1 2Sigma-, and 1 2Delta states lead to the CO + S+(2Du) products representing the second dissociation limit; and the dissociations of the 2 2Pi and 1 2Sigma+ states lead to the CO + S+(2Pu) products representing the third dissociation limit. Seams of the 1 2Pi-1 4Sigma-, 2 2Pi-1 4Sigma-, 2 2Pi-1 2Sigma-, 2 2Pi-1 2Delta, and 1 2Sigma(+)-1 4Sigma- potential energy surface intersections were calculated at the CASPT2 level, and the minima along the seams were located. The calculations indicate that within the experimental energy range (15.07-16.0 eV) the 2 2Pi(A 2Pi) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 1 2Pi followed by the direct dissociation of 1 2Pi forming S+(2Du) and that within the experimental energy range (16.04-16.54 eV) the 1 2Sigma+(B 2Sigma+) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 2 2Pi followed by the predissociation of 2 2Pi by 1 2Sigma- and 1 2Delta forming the S+(2Du) ion. These indications are in line with the experimental fact that both the 4Su and 2Du states of the S+ ion can be formed from the 2 2Pi and 1 2Sigma+ states of the OCS+ ion.

Reaction dynamics of electronically state-specific CH2 with NO

With time-resolved Fourier transform infrared emission spectroscopy and DFT B3LYP quantum calculation, the reaction dynamics of CH2(X 3B1) and CH2(a 1A1) with NO have been investigated. It is found that both 3CH2+NO and 1CH2+NO reactions follow the same reaction pathways and produce same products arising from the same elementary channels. The primary products of vibrationally excited CO(v), HCO(v1), HOCN(v2), OH(v), and NH2(v3) were detected for the first time and four reaction channels have thus been identified. Theoretically, a doublet potential energy surface is characterized. On the potential energy surfaces, both the 3CH2+NO and 1CH2+NO systems reach a crucial intermediate OCHNH via a CNO ring-closure and ring-opening process. From this intermediate, the four reaction pathways proceed: C–N bond rupture in OCHNH simply leads to NH+HCO; OCHNH rearranges either to H2NCO producing CO+NH2, or to HOCHN generating HOCN+H and HCN+OH.

Reaction of Cl with N3: a CAS study

The CAS methods were used for exploring mechanisms of the Cl + N3(X2Π) → NCl(1Δ) + N2 (i) and Cl + N3(X2Π) → NCl(X3Σ−) + N2 (ii) reactions. The CASSCF/cc- pVTZ path calculations indicate that channel (i) occurs in the 1A′ potential energy surface (PES) and there exists an intermediate (IM(1A′)) followed by a transition state along the reaction path and that channel (ii) occurs in the 3A′′ PES and it has a single step with a transition state. The CASPT2/cc-pVTZ energetic results indicate that channel (i) is feasible while channel (ii) is unfeasible. Preliminary exploration for the 1A′–3A′′ PES crossing at the CASSCF/cc-pVTZ level implies that the crossing may not cause predissociation of IM(1A′) into the ground state product (NCl (3Σ−) + N2).

Electronic states of the C6H5CN+ ion studied using multiconfiguration wave functions

Electronic states of the C6H5CN+ ion have been studied within C2v symmetry using the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with an atomic natural orbital basis set. Adiabatic excitation energies (T 0), vertical excitation energies (T v), and relative energies ( ) at the ground-state geometry of the C6H5CN molecule were calculated for eight electronic states of the C6H5CN+ ion. The CASPT2//CASSCF T 0 and CASPT2 T v and calculations all indicate that the 1 2B1, 1 2A2, 2 2B1, 1 2B2, 1 2A1, 2 2A1, 2 2B2, and 3 2B1 states are the eight lowest-lying states of C6H5CN+. In conjunction with the MS-CASPT2 T 0 and oscillator strength f calculations, we assigned the X, A, B, C, D, E, F, and G states of the C6H5CN+ ion to 1 2B1, 1 2A2, 1 2B2, 2 2B1, 1 2A1, 2 2A1, 2 2B2, and 3 2B1, respectively.