Ab initio potential energy surfaces, bound states, and electronic spectrum of the Ar-SH complex

New ab initio potential energy surfaces for the (2)Pi ground electronic state of the Ar-SH complex are presented, calculated at the RCCSD(T)/aug-cc-pV5Z level. Weakly bound rotation-vibration levels are calculated using coupled-channel methods that properly account for the coupling between the two electronic states. The resulting wave functions are analyzed and a new adiabatic approximation including spin-orbit coupling is proposed. The ground-state wave functions are combined with those obtained for the excited (2)Sigma(+) state [D. M. Hirst, R. J. Doyle, and S. R. Mackenzie, Phys. Chem. Chem. Phys. 6, 5463 (2004)] to produce transition dipole moments. Modeling the transition intensities as a combination of these dipole moments and calculated lifetime values [A. B. McCoy, J. Chem. Phys. 109, 170 (1998)] leads to a good representation of the experimental fluorescence excitation spectrum [M.-C. Yang, A. P. Salzberg, B.-C. Chang, C. C. Carter, and T. A. Miller, J. Chem. Phys. 98, 4301 (1993)].     

SiH2Cl2: ab initio anharmonic force field, dipole moments, and infrared vibrational transitions

The vibrational spectra of SiH2Cl2 have been recorded in the 1000-13,000 cm(-1) region, utilizing the Fourier-transform spectroscopy and Fourier-transform intracavity laser absorption spectroscopy. Totally 61 band centers and intensities are derived from the infrared spectra. An ab initio quartic force field is obtained by applying the second-order Moller-Plesset perturbation theory and correlation-consistent polarized valence triplet-zeta basis sets [J. Chem. Phys. 90, 1007 (1989); 98, 1358 (1993)]. Most observed bands are assigned by the vibration analysis based on the second-order perturbation theory. Reduced-dimensional ab initio dipole moment functions (two dimensional and three dimensional) have also been calculated to investigate the absolute band intensities of the SiH2 chromophore. The calculated values agree reasonably with the observed ones.     

Ab initio rotation-vibration spectra of HCN and HNC

We have calculated an ab initio HCN/HNC linelist for all transitions up to J= 25 and 18000 cm(-1) above the zero point energy. This linelist contains more than 200 million lines each with frequencies and transition dipoles. The linelist has been calculated using our semi-global HCN/HNC VQZANO + PES and dipole moment surface, which were reported in van Mourik et al. (J. Chem. Phys. 115 (2001) 3706). With this linelist we synthesise absorption spectra of HCN and HNC at 298 K and we present the band centre and band transition dipoles for the bands which are major features in these spectra. Several of the HCN bands and many of the HNC bands have not been previously studied. Our line intensities reproduce via fully ab initio methods the unusual intensity structure of the HCN CN stretch fundamental (00(0)1) for the first time and also the forbidden (02(2)0) HCN bending overtone. We also compare the J = 1-->0 pure rotational transition dipole in the HCN/HNC ground and vibrationally excited states with experimental and existing ab initio results.     

Radiative transition probabilities, lifetimes and dipole moments for the vibrational levels of the X1Sigma+ ground state of 39K85Rb

Using a potential energy curve (based primarily on the RKR potential of Amiot and Verges [J. Chem. Phys. 112, 7068 (2000)]) and a dipole moment function (based primarily on ab initio calculations of Park et al. [Chem. Phys. 257, 135 (2000)]), we have calculated radiative transition probabilities (Einstein A coefficients), radiative lifetimes, and dipole moment expectation values involving all vibrational levels (for several rotational quantum numbers) of the X1Sigma+ ground state of 39K85Rb. We observe that the radiative lifetimes of vibrationally excited levels, in particular, are approximately 10(3)-10(6) seconds, far too long to be significant in most ultracold experiments involving 39K85Rb or its isotopomers. Comparison with other molecules (LiH and HF) suggests that simple scaling (A approximately mu2nu3 approximately tau(-1)) will predict similarly long lifetimes for many other heteronuclear molecules, e.g., RbCs.     

Measurement of the transition dipole moment of the first hot band of the nu2 mode of the methyl radical by diode laser spectroscopy

The line strengths of five Q-branch lines of the first hot band of the out-of-plane bending vibration (2(1)(2)) of the methyl radical, CH 3, have been measured using infrared laser absorption spectroscopy. The spectra of the radical were measured in situ in a microwave discharge using ditertiary butyl peroxide, diluted in argon as the precursor. The line strengths were used to determine the transition dipole moment of the hot band. Absolute concentrations of the radical were required for this purpose, and these were determined kinetically from the measured decays of the spectral lines after the discharge was extinguished. The translational, rotational, and vibrational temperatures were also determined spectroscopically from measured integrated line intensities and line widths. The transition dipole moment of the first hot band was determined to be 0.31(6) D. This value is in satisfactory agreement with the value of 0.27(3) D from a high-precision ab initio calculation using the self-consistent electron pairs (SCEP) method reported by Botschwina, Flesch, and Meyer [Botschwina, P.; Flesch, J.; Meyer, W. Chem. Phys. 1983, 74, 321].     

Spectroscopy of Ar-SH and Ar-SD. II. Determination of the three-dimensional intermolecular potential-energy surface

All the pure rotational transitions reported in the previous studies [J. Chem. Phys. 113, 10121 (2000); J. Mol. Spectrosc. 222, 22 (2003)] and newly observed rotation-vibration transitions, P = 1/2 <-- 3/2, for Ar-SH and Ar-SD [J. Chem. Phys. (2005), the preceding paper] have been simultaneously analyzed to determine a new intermolecular potential-energy surface of Ar-SH in the ground state. A Schrodinger equation considering the three-dimensional freedom of motion for an atom-diatom complex in the Jacobi coordinate, R, theta, and r, was numerically solved to obtain energies of the rovibrational levels using the discrete variable representation method. A three-dimensional potential-energy surface is determined by a least-squares fitting with initial values of the parameters for the potential obtained by ab initio calculations at the RCCSD(T)/aug-cc-pVTZ level of theory. The potential well reproduces all the observed data in the microwave and millimeter wave regions with parity doublings and hyperfine splittings. Several low-lying rovibrational energies are calculated using the new potential-energy surface. The dependence of the interaction energy between Ar and SH(2pi(i)) on the bond length of the SH monomer is discussed.     

Three-dimensional potential energy surface of the Ar-OH(2Pi i) complex

Pure rotational transitions in the ground state for Ar-OH and Ar-OD [Y. Ohshima et al., J. Chem. Phys. 95, 7001 (1991) and Y. Endo et al., Faraday Discuss. 97, 341 (1994)], those in the excited states of the OH vibration, nu(s)=1 and 2, observed by Fourier-transform microwave spectroscopy in the present study, rotation-vibration transitions observed by infrared-ultraviolet double-resonance spectroscopy [K. M. Beck et al., Chem. Phys. Lett. 162, 203 (1989) and R. T. Bonn et al., J. Chem. Phys. 112, 4942 (2000)], and the P-level structure observed by stimulated emission pumping spectroscopy [M. T. Berry et al., Chem. Phys. Lett. 178, 301 (1991)] have been simultaneously analyzed to determine the potential energy surface of Ar-OH in the ground state. A Schrodinger equation, considering all the freedom of motions for an atom-diatom system in the Jacobi coordinate, R, theta, and r, was numerically solved to obtain energies of the rovibrational energy levels using the discrete variable representation method. A three-dimensional potential energy surface is determined by a least-squares fitting. In the analysis the potential parameters, obtained by ab initio calculations at the RCCSD(T) level of theory with a set of basis functions of aug-cc-pVTZ and midbond functions, are used as initial values. The determined intermolecular potential energy surface and its dependence on the OH monomer bond length are compared with those of an isovalent radical complex, Ar-SH.     

A new ab initio ground-state dipole moment surface for the water molecule

A valence-only (V) dipole moment surface (DMS) has been computed for water at the internally contracted multireference configuration interaction level using the extended atom-centered correlation-consistent Gaussian basis set aug-cc-pV6Z. Small corrections to these dipole values, resulting from core correlation (C) and relativistic (R) effects, have also been computed and added to the V surface. The resulting DMS surface is hence called CVR. Interestingly, the C and R corrections cancel out each other almost completely over the whole grid of points investigated. The ground-state CVR dipole of H(2) (16)O is 1.8676 D. This value compares well with the best ab initio one determined in this study, 1.8539+/-0.0013 D, which in turn agrees well with the measured ground-state dipole moment of water, 1.8546(6) D. Line intensities computed with the help of the CVR DMS shows that the present DMS is highly similar to though slightly more accurate than the best previous DMS of water determined by Schwenke and Partridge [J. Chem. Phys. 113, 16 (2000)]. The influence of the precision of the rovibrational wave functions computed using different potential energy surfaces (PESs) has been investigated and proved to be small, due mostly to the small discrepancies between the best ab initio and empirical PESs of water. Several different measures to test the DMS of water are advanced. The seemingly most sensitive measure is the comparison between the ab initio line intensities and those measured by ultralong pathlength methods which are sensitive to very weak transitions.     

A post-Hartree-Fock model of intermolecular interactions: inclusion of higher-order corrections

We have previously demonstrated that the dipole moment of the exchange hole can be used to derive intermolecular C(6) dispersion coefficients [J. Chem. Phys. 122, 154104 (2005)]. This was subsequently the basis for a novel post-Hartree-Fock model of intermolecular interactions [J. Chem. Phys. 123, 024101 (2005)]. In the present work, the model is extended to include higher-order dispersion coefficients C(8) and C(10). The extended model performs very well for prediction of intermonomer separations and binding energies of 45 van der Waals complexes. In particular, it performs twice as well as basis-set extrapolated MP2 theory for dispersion-bound complexes, with minimal computational cost.     

Comment on "anharmonic properties of the vibrational quantum computer" [J. Chem. Phys. 126, 204102 (2007)

Suitable molecules for quantum computing cannot be discussed in terms of anharmonicity and CNOT gates alone. The validity of the approximate approach [M. Zhao and D. Babikov, J. Chem. Phys.126, 204102 (2007)] is limited. Frequencies and anharmonicities cannot be used independent from the molecule. Hermite polynomials with the linear approximation for the dipole moment lead to oversimplified gates with potentially low intensities.     

Soft sticky dipole-quadrupole-octupole potential energy function for liquid water: an approximate moment expansion

A new, efficient potential energy function for liquid water is presented here. The new model, which is referred here as the soft sticky dipole-quadrupole-octupole (SSDQO) model, describes a water molecule as a Lennard-Jones sphere with point dipole, quadrupole, and octupole moments. It is a single-point model and resembles the hard-sphere sticky dipole potential model for water by Bratko et al. [J. Chem. Phys. 83, 6367 (1985)] and the soft sticky dipole model by Ichiye and Liu [J. Phys. Chem. 100, 2723 (1996)] except now the sticky potential consists of an approximate moment expansion for the dimer interaction potential, which is much faster than the true moment expansion. The object here is to demonstrate that the SSDQO potential energy function can accurately mimic the potential energy function of a multipoint model using the moments of that model. First, the SSDQO potential energy function using the dipole, quadruple, and octupole moments from SPC/E, TIP3P, or TIP5P is shown to reproduce the dimer potential energy functions of the respective multipoint model. In addition, in Monte Carlo simulations of the pure liquid at room temperature, SSDQO reproduces radial distribution functions of the respective model. However, the Monte Carlo simulations using the SSDQO model are about three times faster than those using the three-point models and the long-range interactions decay faster for SSDQO (1/r(3) and faster) than for multipoint models (1/r). Moreover, the contribution of each moment to the energetics and other properties can be determined. Overall, the simplicity, efficiency, and accuracy of the SSDQO potential energy function make it potentially very useful for studies of aqueous solvation by computer simulations.     

Rovibrational spectra of LiH2+, LiHD+ and LiD2+ determined from FCI property surfaces

Full configuration interaction (FCI) has been used in conjunction with the lithium [6s5p3d1f] (Iron, M. A.; et al. Mol. Phys. 2004, 101, 1345) and hydrogen aug-cc-pVTZ basis sets to construct an 83-point potential energy surface of the 1A1 ground state of 7LiH2+. Vibrational and rovibrational wave functions of the (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+ ground states were calculated variationally using an Eckart-Watson Hamiltonian. For (7)LiD2+, rovibrational transition frequencies for K = 0, 1, 2 and J < or = 10 are within ca. 0.1% of recent experimental values (Thompson, C. D.; et al. J. Chem. Phys. 2006, 125, 044310). A 47-point FCI dipole moment surface was embedded in the rovibrational Hamiltonian to calculate vibrational and rovibrational radiative properties. At 296 K, with v < or = 4 and J < or = 4, the 2(02) <-- 3(03) rotational transition in the |001> band was found to have the greatest spectral intensity with respect to the ground electronic states of (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+. In each case, the most intense rovibrational transitions have been assigned unequivocally using the J, Ka, Kc assignment scheme.     

Ab initio large-amplitude quantum-tunneling dynamics in vinyl radical: a vibrationally adiabatic approach

Large-amplitude tunneling in vinyl radical over a C2v planar transition state involves CCH bending excitation coupled to all other internal coordinates, resulting in a significant dependence of barrier height and shape on vibrational degrees of freedom at the zero-point level. An ab initio potential surface for vinyl radical has been calculated at the CCSD(T) level (AVnZ; n=2, 3, 4, 5) for vibrationally adiabatic 1D motion along the planar CCH bending tunneling coordinate, extrapolated to the complete basis set (CBS) limit and corrected for anharmonic zero-point effects. The polyatomic reduced moment of inertia is calculated explicitly as a function of tunneling coordinate, with eigenvalues and tunneling splittings obtained from numerical solution of the resulting 1D Schr?dinger equation. Linear scaling of the CBS potential to match predicted and observed tunneling splittings empirically yields an adiabatic barrier height of DeltaEadiab=1696(20) cm(-1) which, when corrected for zero-point energy contributions, translates into an effective barrier of DeltaEeff=1602(20) cm(-1) consistent with estimates (DeltaE=1580(100) cm(-1)) by Tanaka and coworkers [J. Chem. Phys., 2004, 120, 3604-3618]. These zero-point-corrected potential surfaces are used to predict tunneling dynamics in vibrationally excited states of vinyl radical, providing strong support for previous jet-cooled high-resolution infrared studies [Dong et al., J. Phys. Chem. A, 2006, 110, 3059-3070] in the symmetric CH2 stretch mode.     

Van der Waals interactions in solids using the exchange-hole dipole moment model

The exchange-hole dipole moment model of dispersion interactions of Becke and Johnson [J. Chem. Phys. 127 154108 (2007)] is implemented for calculations in solids using the pseudopotentials/plane-waves approach. The resulting functional retains the simplicity and efficiency of semilocal functionals while accurately treating dispersion interactions via a semiempirical asymptotic expansion. The dispersion coefficients are calculated completely ab initio using local quantities alone (density, gradient, Laplacian, and kinetic energy density). The two empirical parameters in the damping function are calculated by fit to a 65-molecule training set recalculated under periodic boundary conditions. Calculations in simple solids offer good results with minimal computational cost compared to electronic relaxation.     

Time-dependent wave packet study on trans-cis isomerization of HONO driven by an external field

The present paper is devoted to a full quantum mechanical study of the cis-->trans isomerization of HONO. In contrast to our previous study [Richter et al., J. Chem. Phys. 120, 6072 (2004)], the dynamics is now performed in the presence of an external time-dependent field in order to be closer to experimental conditions. A six-dimensional dipole surface is computed. Using a previously developed potential energy surface [Richter et al., J. Chem. Phys. 120, 1306 (2004)], all eigenstates up to 4000 cm(-1) are calculated. We simulate the dynamics during and after excitation by an electromagnetic pulse whose parameters are chosen to efficiently trigger the isomerization. Our investigations show that there is a selective isomerization pathway.     

Vibrational structure and methyl C-H dynamics in propyne

Our previous study [J. Chem. Phys. 122, 224316 (2005)] presented the photoacoustic and action spectra of the V=2, 3, 4, and 5 manifolds of the C-H methyl stretching vibrations of propyne and their analysis in terms of a simplified joint local mode/normal mode model. In the current paper the C-H transition intensities were calculated using B3LYP6-311++G(d,p) level of theory to obtain the dipole moment functions. The diagonalization of the vibrational Hamiltonian revealed new model parameters obtained by least square fitting of the eigenvalues to the action spectra band origins, while examining the correspondence between the calculated intensities and simulated band areas. The newly derived parameters predict well the band positions and the observed intensities, allowing new assignment of the features. The derived Hamiltonian was also used to obtain the overall temporal behavior of the C-H stretches as a result of the Fermi couplings and interactions with the bath states. These results indicate that any specificity attained by suitable excitation of the methyl C-H stretches is lost on picosecond time scale, primarily due to strong interactions with doorway states in the lower overtone and coupling with bath states in the region of the higher ones.     

Charge transfer stabilization of an excess electron on a molecular surface

In a developed molecular surface model (Jalbout and Adamowicz, Mol Phys, 2006, 19, 3101), we suggested a series of cyclohexane and cyclooctane systems with a hydrogen‐bonded network of OH groups on one side of the surface and hydrogen atoms on the opposite side. The OH groups in this work increased the dipole moment of the complexes in order to form stable dipole bound anions. In this report we consider the dipole‐bound and solvated anions between a set of hypothetical molecular surfaces and NH₃BF₃. The resulting complexes are stable with respect to vertical electron detachment. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

On the interaction of electrons with betaine zwitterions

Betaine is a permanent zwitterion. The molecular betaine anion has been generated in a hybrid, infrared desorption-electron photoemission source and its photoelectron spectrum recorded. The photoelectron spectrum of the betaine anion is characteristic of a dipole bound anion, and its vertical detachment energy was measured to be 0.29+/-0.03 eV. Calculations by Rak, Skurski, and Gutowski [J. Chem. Phys. 114, 10673 (2001)] had found the betaine anion to be a dipole bound anion with a vertical detachment energy of 0.28 eV. We also measured the vertical detachment energy of deprotonated betaine to be approximately 1.9 eV.     

Full-dimensional vibrational calculations for H5O2+ using an ab initio potential energy surface

We report quantum diffusion Monte Carlo (DMC) and variational calculations in full dimensionality for selected vibrational states of H(5)O(2) (+) using a new ab initio potential energy surface [X. Huang, B. Braams, and J. M. Bowman, J. Chem. Phys. 122, 044308 (2005)]. The energy and properties of the zero-point state are focused on in the rigorous DMC calculations. OH-stretch fundamentals are also calculated using "fixed-node" DMC calculations and variationally using two versions of the code MULTIMODE. These results are compared with infrared multiphoton dissociation measurements of Yeh et al. [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)]. Some preliminary results for the energies of several modes of the shared hydrogen are also reported.     

Quadrupole moment function and absolute infrared quadrupolar intensities for N2

High level ab initio methods have been used to calculate values of the quadrupole moment of the ground X (1)Sigmag+ state of N2 on a dense radial mesh spanning the interval of 0.8-12.1 a.u. Detailed convergence tests indicate that the resulting equilibrium values of the quadrupole moment Theta(e)=-1.1273 a.u. and its first radial derivative dTheta(R)/dR/e=0.9604 a.u. have absolute uncertainties of 0.3% and 0.8%, respectively, and are more accurate than the best experimental values of these quantities. The calculated quadrupole moment function, together with a recently reported accurate analytic empirical potential energy function [Le Roy et al., J. Chem. Phys. 125, 164310 (2006)], is used to generate values of the radial matrix elements determining the absolute intensities of infrared vibration-rotation transitions of ground-state N2, which take full account of vibration-rotation interactions. These results should improve the reliability of the interpretations of N2 contributions to infrared atmospheric spectra.