The Weak Interaction on CO_2...CO van der Waals Complex: A Theoretical Study

The geometries of van der Waals complex CO 2...CO were optimized at DFT and second order Moller Plesset perturbation(MP2) levels with the large basis set, three stable structures were found. The most stable structure has a T shape geometry in which the CO lies along the C 2 axis of CO 2, with the two C atoms direct contact and R (C...C)=0 3227 nm. The corresponding energies of the most stable structure were calculated by means of MP2, MP4D, MP4DQ, MP4SDTQ, MP4SDQ, CCSD and CCSD(T) methods. The BSSE(basis set superposition error) was eliminated by the Boys Bernardi counterpoise correction(CP) method. According to thermodynamics data, van der Waals complex CO 2...CO can be found at a low temperature and/or a high pressure. There is a little charge transferred between the two interacted subunits. In the most stable structure, CO 2 is the acceptor and CO is the donor.

Infrared diode laser spectroscopy of O_2–N_2O van der Waals complex in the v_1 symmetric stretch region of N_2O

The rovibrational spectrum of O2–N2O van der Waals complex is measured in the ν1 symmetric stretch region of N2 O monomer using a tunable diode laser spectrometer. The complex is generated by a slit-pulsed supersonic expansion with gas mixtures of O2, N2 O, and He. Both a- and b-type transitions are observed. The effective Hamiltonian for an open-shell complex consisting of a diatomic molecule in a ^3Σ electronic state and a closed-shell partner is used to analyze the observed spectrum. Molecular constants in the vibrationally excited state are determined accurately. The band-origin of the spectrum is determined to be 1284.7504（25） cm^-1, red-shifted from that of the N2 O monomer by ～ 0.1529 cm^-1.

Theoretical Study on the Rotational Spectra of Ar-D232S Complex

We report a theoretical study on the rotational spectra of Ar-D232S. The intermolecular po- tential energy surface was transformed from our latest ab initio three-dimensional potential of Ar-H232S. The rotational energy levels and wavefunctions of the complex were calcu- lated by using the radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm. The calculated rotational transition frequencies and structural parameters were found to be in good agreement with the available experimental values.

The Role of High Excitations in Constructing Sub-spectroscopic Accuracy Intermolecular Potential of He-HCN： Critically Examined by the High-Resolution Spectra with Resonance States

Interpreting high-resolution rovibrational spectra of weakly bound complexes commonly requires spectroscopic accuracy （〈1 cm-1） potential energy surfaces （PES）. Constructing high-accuracy ab initio PES relies on the high-level electronic structure approaches and the accurate physical models to represent the potentials. The coupled cluster approaches including single and double excitations with a perturbational estimate of triple excitations （CCSD（T）） have been termed the ＂gold standard＂ of electronic structure theory, and widely used in generating intermolecular interaction energies for most van der Waals complexes. However, for HCN-He complex, the observed millimeter-wave spectroscopy with high-excited resonance states has not been assigned and interpreted even on the ab initio PES computed at CCSD（T） level of theory with the complete basis set （CBS） limit. In this work, an effective three-dimensional ab initio PES for HCN-He, which explicitly incorporates dependence on the Q1 （C-H） normal-mode coordinate of the HCN monomer has been calculated at the CCSD（T）/CBS level. The post-CCSD（T） interaction energy has been examined and included in our PES. Analytic two-dimensional PESs are obtained by least-squares fitting vibrationally averaged interaction energies for v1 （C-H）=0, and 1 to the Morse/Long-Range potential function form with root-mean-square deviations （RMSD） smaller than 0.011 cm-1. The role and significance of the post-CCSD（T） interaction energy contribution are clearly illustrated by comparison with the predicted rovibrational energy levels. With or without post-CCSD（T） corrections, the value of dissociation limit （Do） is 8.919 or 9.403 cm-1, respectively. The predicted millimeter-wave transitions and intensities from the PES with post-CCSD（T） excitation corrections are in good agreement with the available experimental data with RMS discrepancy of 0.072 cm-1. Moreover, the infrared spectrum for HCN-He complex is predicted for the first time. These results will serve as a good starting point and provide reliable guidance for future infrared studies of HCN doped in （He）n clusters.

A local spin study for magnetic model complex HHeH

Davidson and Clark’s equations for calculating the local spin of molecules were rewritten and simplified as matrices algebra. By applying our program, we calculated the local spin of O2 and NO molecules and obtained almost the same results as those by Davidson and Clark’s method. The local spin and the magnetic coupling constant J of the simple Van der Waals complex HHeH were calculated as well to investigate the relationship between the geometric structures and magnetic values.