| Since state-to-state dynamical characterization of triatomic molecular reactions is desired, it is clear that a better understanding of these systems cannot be achieved without an accurate potential energy surfaces (PESs), which provide a reliable platform for studies of the reaction dynamics. In this work, we have constructed global potential energy surfaces for the first excited (A2A') state of HO2 and three lowest lying electronic states (X1A', A1 A?and (?)3 A?) of the HNO systems by using high-lever ab initio calculations. Based on the calculated potential energy surfaces, the vibrational bound states of the molecules were obtained by employing the efficient Lanczos algorithm.For the HO2 system, a global PES was developed by spline fitting 17000 ab initio points at the internal contracted multireference configuration interaction (icMRCI) level with Davidson correction using the augmented correlation-consistent polarized valence quadruple zeta (AVQZ) basis set. The calculated dissociation energies for De(H-OO) and De(O-OH) on the PES are 56.20 and 46.35 kcal/mol, respectively. The zero-point energy corrected values, Do(H-OO) and Do(O-OH), are 50.18 and 43.51 kcal/mol, respectively, which are in good agreement with the experimental values of 50.39 and 44.13 kcal/mol. Our results indicate that the PES reported in this work is accurate and well suited for studying the reaction dynamics of H(2S)+O2((?)1?g)(?) OH(X2?)+O(3P). In addition, we focus on low-lying vibrational states of HO2 (A2 A'). The calculated fundamental frequency for O-O stretching mode (v3=927.95 cm-1) is in excellent agreement with the more recent value (929.068 cm-1), but for the other two modes (v1=3566.72 cm-1 and v2=1196.22 cm-1) are much different from the experimental values namely 3268.5 and 1285 cm-1, respectively. The discrepancy between values for V1 calculated by high-level methods used in this studv and exneriment of about 300 cm-1 clearlv indicates a mis-assignment. And we conclude that the two frequencies listed in the Jacox table for HO2(A2A') are incorrect and need to be updated.The PESs for the three lowest lying electronic states of the HNO systems were constructed separately. The global PES for the lowest triplet electronic state (a3A") of HNO has been developed by a three-dimensional cubic spline interpolation of more than 13,000 ab initio points, which were also calculated at the icMRCI level with Davidson correction using the augmented correlation-consistent polarized valence quintuple zeta (AV5Z) basis set. The calculated dissociation energy without the zero-point energy correction, De(H-NO), is 1.484 eV, which is only 0.06 eV higher than the experimental values of 1.424±0.013 eV. To highlight the key region for the reaction dynamics of N(4S)+OH(X2?)?H(2S)+NO(X2?), an especially long grid was used to map out the N+OH asymptotic region. The calculated endothermicity of 1.978 eV is much closed to the experimental values of 2.004±0.043eV. To ascertain the quality of the new PES, low-lying vibrational energy levels of the HNO and HON isomers as well as their isotopomers were calculated using the Lanczos algorithm. It is shown that the overall agreement with experimental vibrational frequencies is very good.For the signlet electronic states XA'and A1 A?of HNO, we have chosen the similar method described above for the a3 A" state PES to construct the two PESs. The only difference is the replacement of AV5Z basis set with AVQZ. The global minimum of the ground state PES was found to be located at rNO=2.286 a0, rNH=1.986 a0, and?H.N.O=108.3°, which is in good agreement with the experimental and computational values. The calculated dissociation energy including zero-point energy corrections for Do(H-NO) was found to be 2.035 eV, which is in much better agreement with the experimental values of 2.0395±0.0012 eV than those of the previous calculations. And the electronic origin of the transition between the A and X states was found to be 13371 cm-1, which is in much better agreement with the experimental value of 13153 cm-1 than the previous theoretical result of 13985 cm-1. In order to investigate the influence of RT effect on the vibrational states of the system, we also calculated the matrix elements of the electronic angular momentum Lz. and L.z at the state-averaged complete active space self-consistent field (CASSCF) level. The low-lying vibrational energy levels with and without the diagonal RT terms for the X1A'and A1 A" states of both HNO and HON isomers are obtained using the new ab initio PESs. Unlike the ground state, the RT effect becomes important for the higher bending states on the A1 A" state. When the RT coupling is not taken into account, the calculated vibrational level for the bending excited state (0,0,3) is lower about 30 cm-1 than the observed value. The addition of the diagonal RT terms slightly improves the stretching frequencies, but the calculated energies are in much better agreement with the experimental data for the bending energy levels. For instance, the calculated frequencies for the bending states (0,0,2) and (0,0,3) (1957.77 and 2933.07 cm-1) are in excellent agreement with the experimental band origins (1959.4 and 2932.2 cm-1). The new PESs represent a significant improvement over the previous PESs in that the better agreement with experimental thermodynamic data was achieved, and well suited for studying the state-to-state dynamics of the important reaction H(2S)+NO(X2?)<-> O(3P)+NH(X3?-)... |
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