A new potential energy surface and rovibrational spectra of the CO-CO2 complex: Dependence on the antisymmetric stretching vibration of CO2

We present a new ab initio five-dimensional potential energy surface for the CO-CO2 complex containing the Q3 normal mode for the ν3 asymmetric stretching vibration of the CO2 unit. The potential was calculated by supermolecular approach at the CCSD(T)-F12 level with aug-cc-pVTZ basis set plus midpoint bond functions. Two vibrationally averaged four-dimensional potentials for CO-CO2 with CO2 in the ground and ν3 excited states were generated by the integration of the five-dimensional potential over the Q3 intramolecular coordinate. Each potential displays a T-shaped global minimum with the C end in the CO unit pointing toward the C atom in the CO2 unit and a T-shaped local minimum but with the CO monomer rotated by 180º. The rovibrational bound states and energy levels for the CO-CO2 dimer were obtained employing the radial discrete variable representation (DVR)/angular finite basis representation (FBR) method in conjunction with the Lanczos algorithm. The vibrational ground and some lower excited states for CO-CO2 are localized around the global minimum because of the higher potential barriers. The band origin is blueshifted by 0.2089 cm-1 for CO-CO2 in the CO2 ν3 range, which is consistent with the experimental result of 0.211 cm-1. The geared bending vibrational frequencies for CO-CO2 are 24.7101 and 24.5549 cm-1 at the ground and ν3 excited states of CO2, respectively. The predicted rovibrational frequencies as well as spectral constants coincide with the available observations, and these parameters show the CO-CO2 complex is a nearly prolate asymmetric rotor.

Nonadiabatic fragmentation of H2O+ and isotopomers. Wave packet propagation using ab initio wavefunctions

The nonadiabatic fragmentation of excited water cations (and isotopomers) is studied by propagating wave packets on ab initio potential energy surfaces.

POTENTIAL ENERGY SURFACES AND MICROWAVE SPECTRA FOR 20Ne–13C16O2, 22Ne–12C16O2 and 22Ne–13C16O2 COMPLEXES

We report averaged potential energy surfaces for isotopic Ne–CO2 complexes (20 Ne –13 C 16 O 2, 22 Ne –12 C 16 O 2 and 22 Ne –13 C 16 O 2). According to the latest ab initio potential of 20 Ne –12 C 16 O 2 (Chen R, Jiao EQ, Zhu H, Xie DQ, J Chem Phys133:104302, 2010) including the Q3 normal mode for the υ3 antisymmetric stretching vibration of the CO2 molecule. We obtain the averaged potentials for 20 Ne –13 C 16 O 2, 22 Ne –12 C 16 O 2 and 22 Ne –13 C 16 O 2 by the integration of the three-dimensional potential over the Q3 coordinate. The averaged potential surfaces are found to have a T-shaped global minimum and two equivalent linear local minima. The radial DVR/angular FBR method and the Lanczos algorithm are applied to calculate the rovibrational energy levels. Comparison with the available observed values showed an overall excellent agreement for all spectroscopic parameters and the microwave spectra.

Ab Initio Potential Energy Surfaces for Both the Ground (X̃1A′) and Excited (A∼1A′′) Electronic States of HSiBr and the Absorption and Emission Spectra of HSiBr/DSiBr

Ab initio potential energy surfaces for the ground (X̃1A′) and excited (A˜A′′1) electronic states of HSiBr were obtained by using the single and double excitation coupled-cluster theory with a noniterative perturbation treatment of triple excitations and the multireference configuration interaction with Davidson correction, respectively, employing an augmented correlation-consistent polarized valence quadruple zeta basis set. The calculated vibrational energy levels of HSiBr and DSiBr of the ground and excited electronic states are in excellent agreement with the available experimental band origins. In addition, the absorption and emission spectra of HSiBr and DSiBr were calculated using an efficient single Lanczos propagation method and are in good agreement with the available experimental observations.

THEORETICAL STUDIES OF $\tilde{A}{}^1 A^{\prime\prime}\to\tilde{X}{}^1 A^\prime$ RESONANCE EMISSION SPECTRA OF HCN/DCN USING SINGLE LANCZOS PROPAGATION METHOD

Using an efficient single Lanczos propagation method, we report the [Formula: see text] resonance emission spectra of HCN and DCN from a number of low-lying vibrational levels of the Ã-state manifold. Our calculations represent the first such undertaking in which a high-quality ab initio based potential energy surface of the excited (Ã1 A″) state and a [Formula: see text] transition dipole surface were used. The results show a significant improvement over previous theoretical work in reproducing experimental stimulated emission pumping spectra of HCN. The improved theory-experiment agreement is attributed to the accurate Ã-state potential energy surface, while the impact of the transition dipole function was found to be relatively minor.

LANCZOS ALGORITHMS AND CROSS CORRELATION FUNCTIONS Cif(E)

Cross correlation (CC) functions Cif(E) play an important role in chemical physics. They appear in the description of reactive scattering, photo-dissociation, photo-electron spectroscopy and electron transfer to mention a few. In this paper, we discuss two methods based on the Lanczos algorithm to compute the CC function for several initial and final states at the same time, without diagonalization. The property of the coupled two-term recursions variant of the Lanczos algorithm that yields a decomposition [Formula: see text] of the tridiagonal Lanczos matrix is crucial. The first method, the quasi minimal-recursive residue generation method (QM-RRGM) is based on solving a set of linear equations whereas the second method is based on a band-Lanczos method. The computational cost is of the same order of magnitude for both methods and is given by the number of matrix-vector multiplications in the underlying Lanczos method. Only a small set of scalars needs to be updated each recursion. The methods are compared for a model problem, the continuum resonance Raman cross section for a collinear model of CH2IBr . Both methods shows similar convergence properties. By adding a pre-conditioner, the rate of convergence can be increased dramatically.

VIBRATIONALLY AVERAGED POTENTIAL ENERGY SURFACES AND PREDICTED INFRARED SPECTRA OF THE He–18O13C18O AND He–16O13C16O COMPLEXES

Vibrationally averaged potential energy surfaces for isotopic He–CO 2 complexes ( He –18 O 13 C 18 O and He –16 O 13 C 16 O ) are presented. Based on the latest ab initio potential of He –16 O 12 C 16 O (Ran H, Xie D, J Chem Phys128:124323, 2008.) including the Q3 normal mode for the v3 antisymmetric stretching vibration of the CO 2 molecule, the averaged potentials for both He –18 O 13 C 18 O and He –16 O 13 C 16 O are obtained by integrating the potential energy surfaces over the Q3 normal mode. The averaged potentials have T-shaped global minima and two equivalent linear local minima. The radial discrete variable representation/angular finite basis representation method and Lanczos algorithm are employed to calculate the related rovibrational energy levels. The calculated band origin shifts of He –18 O 13 C 18 O and He –16 O 13 C 16 O are 0.1066 and 0.0914 cm-1, respectively, which agree very well with the observed values of 0.1123 and 0.0929 cm-1. The calculated rovibrational transitions of He –18 O 13 C 18 O and He –16 O 13 C 16 O are also in very good agreement with the available experimental spectra.

A new potential energy surface and predicted infrared spectra of the Ar-CO(2) van der Waals complex

A new potential energy surface for Ar-CO(2) is constructed at the coupled-cluster singles and doubles with noniterative inclusion of connected triple [CCSD(T)] level with augmented correlation-consistent triple-zeta (aug-cc-pVTZ) basis set plus midpoint bond functions. The Q(3) normal mode for the v(3) antisymmetric stretching vibration of CO(2) is involved in the construction of the potential. Effective two-dimensional potentials with CO(2) in the ground and first excited v(3) vibrational states are obtained by averaging a three-dimensional potential for each case over the Q(3) asymmetric stretch vibrational coordinate. Both potentials have only a T-shaped minimum with a well depth of 200.97 and 201.37 cm(-1), respectively. No linear local minima are detected. The radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm are employed to calculate the related rovibrational energy levels. The calculated band origin shift of the complex agrees very well with the observed one (-0.474 versus -0.470 cm(-1)). In addition, the predicted infrared spectra based on the two averaged potentials are in excellent agreement with the available experimental data, which again testifies the accuracy of the new potentials.

Reduced-Order Modeling, Error Estimation, and the Role of the Start-Vector: The Recursive Residue Generation Method Revisited

The recursive residue generation method (RRGM) [Wyatt, R. E. Adv. Chem. Phys. 1989, 73, 231] is re-derived using the formalism of reduced-order modeling [Bai, Z. Appl. Numerical Math. 2002, 43, 9]. A stopping criteria for the RRGM recursions is proposed, on the basis of an expression for an upper bound to the absolute error [Bai, Z.; Ye, Q. Electron. Trans. Numerical Anal. 1998, 7, 1]. It is further pointed out that, in general, the start-vector has a negligible effect on the convergence of the RRGM.

Analysis of the HO2 Vibrational Spectrum on an Accurate Ab Initio Potential Energy Surface

The complete vibrational spectrum of the HO2(X(2)A' ') radical, up to the H + O2 dissociation limit, has been determined quantum mechanically on an accurate potential energy surface (PES), based on approximately 15000 ab initio points at the icMRCI+Q/aug-cc-pVQZ level of theory. The vibrational states are found to be assignable at low energies but become more irregular as the energy approaches the dissociation limit. However, even at very high energies, regularity still exists, in sharp contrast to earlier results based on the double many-body expansion (DMBE) IV potential. Several Fermi resonances have been identified, and the spectrum is fit with a spectroscopic Hamiltonian. In addition, the vibrational dynamics is analyzed using a periodic orbit approach.

Five-dimensional ab initio potential energy surface and predicted infrared spectra of H2–CO2 van der Waals complexes

The authors present a new five-dimensional potential energy surface for H2-CO2 including the Q3 normal mode for the nu3 antisymmetric stretching vibration of the CO2 molecule. The potential energies were calculated using the supermolecular approach with the full counterpoise correction at the CCSD(T) level with an aug-cc-pVTZ basis set supplemented with bond functions. The global minimum is at two equivalent T-shaped coplanar configurations with a well depth of 219.68 cm-1. The rovibrational energy levels for four species of H2-CO2 (paraH2-, orthoH2-, paraD2-, and orthoD2-CO2) were calculated employing the discrete variable representation (DVR) for radial variables and finite basis representation (FBR) for angular variables and the Lanczos algorithm. Our calculations showed that the off-diagonal intra- and intermolecular vibrational coupling could be neglected, and separation of the intramolecular vibration by averaging the total Hamiltonian with the wave function of a specific vibrational state of CO2 should be a good approximation with high accuracy. The calculated band origin shift in the infrared spectra in the nu3 region of CO2 is -0.113 cm-1 for paraH2-CO2 and -0.099 cm-1 for orthoH2-CO2, which agrees well with the observed values of -0.198 and -0.096 cm-1. The calculated rovibrational spectra for H2-CO2 are consistent with the available experimental spectra. For D2-CO2, it is predicted that only a-type transitions occur for paraD2-CO2, while both a-type and b-type transitions are significant for orthoD2-CO2.

Three-dimensional ab initio potential-energy surface and rovibrational spectra of the H2–Kr complex

We report a three-dimensional ab initio potential-energy surface for the H2-Kr complex calculated using a supermolecular method. The electronic calculations were performed at the coupled-cluster singles and doubles level with noniterative inclusion of connected triples levels with a large basis set including midbond functions and the full counterpoise correction for the basis-set superposition error. The intermolecular potential energy between the H2 molecule and the Kr atom were evaluated at five potential-optimized discrete variable representation (DVR) grid points generated from the potential-energy curve of H2. The potential for other bond lengths of H2 could be deduced using polynomial interpolations. The complex is found to have a linear preferred structure with a rather flat energy barrier. The three-dimensional DVR method and the Lanczos propagation algorithm were employed to calculate the rovibrational states without separating the inter- and intramolecular nuclear motions. In addition, the rovibrational spectra from the H2 fundamental vibrational band were calculated. The calculated shift for the band origin is -1.50 cm-1, which is in good agreement with the experimental value of -1.706 cm-1, and the calculated transition frequencies in Q1(0) and S1(0) bands are within 3% of the observed values.

Intermolecular potential energy surface and rovibrational spectra of the He–N2O complex from ab initio calculations

We report an ab initio intermolecular potential energy surface calculation on the He-N(2)O complex with N(2)O at its ground state using a supermolecular approach. The calculation was performed at the coupled-cluster [CCSD(T)] level, with the full counterpoise correction for the basis set superposition error and a large basis set including midpoint bond functions. The CCSD(T) potential is found to have two minima corresponding to the T-shaped and linear He-ONN structures. The T-shaped minimum is the global minimum. The two-dimensional discrete variable representation method was employed to calculate the rovibrational energy levels for (4)He-N(2)O and (3)He-N(2)O with N(2)O at its ground and nu(3) excited states. The results indicate that the CCSD(T) potential supports five and four vibrational bound states for the (4)He-N(2)O and (3)He-N(2)O, respectively. Moreover, the calculations on the line intensities of the rotational transitions in the nu(3) region of N(2)O for the ground vibrational state shows that the (3)He-N(2)O spectrum is dominated by a-type transitions (DeltaK(a)=0), while the (4)He-N(2)O spectrum is contributed by both the a-type and b-type (DeltaK(a)=+/-1) transitions. The calculated transition frequencies and the intensities are in good agreement with the observed results.