Jeremy M. Hutson

Vibrational dependence of the anisotropic intermolecular potential of Ar–HF

A new intermolecular potential for Ar–HF is obtained by fitting to results from high‐resolution microwave, far‐infrared, and infrared spectroscopy. The new potential, designated H6(4,3,2), is a function of the diatom mass‐reduced vibrational quantum number η=(v+ (1)/(2) )/(μHX)1/2 as well as the intermolecular distance R and angle θ, and has 22 adjustable parameters. It reproduces all the available spectroscopic data for levels of Ar–HF correlating with HF, v=0, 1, and 2, and DF, v=0 and 1. The H6(4,3,2) potential is qualitatively similar to previous potentials, with a linear Ar–H–F equilibrium geometry and a secondary minimum at the linear Ar–F–H geometry. Compared to the potential of Nesbitt et al. [J. Chem. Phys. 90, 4855 (1989)], obtained from spectra of Ar–HF (v=1), the H6(4,3,2) potential is rather deeper near the equilibrium geometry (Ar–H–F), but shallower around the secondary minimum (Ar–F–H). The absolute well depth increases by 19 cm−1 between HF v=0 and v=1. The vibrationally averaged inductio...

Improved potential energy surfaces for the interaction of H2 with Ar, Kr, and Xe

A combined analysis of discrete infrared and microwave spectra, elastic and inelastic differential cross section measurements, and virial coefficient data has been used to determine improved potential energy surfaces for the H2–Ar, –Kr, and –Xe systems. Key improvements over previous surfaces for these species are an improved delineation of the diatom bond length dependence of the potential anisotropy, and the first experimental determination of a distinct P4(cos θ) anisotropy for an atom–diatom system. The effective anisotropy strength seen by bound state properties (such as transition frequencies) is found to increase from H2–Ar to H2–Kr to H2–Xe, although that seen by properties sensitive to the short‐range potential (such as rotational predissociation and rotational inelasticity) decreases along this series. This reflects the lack of conformality of the various potentials; however, both these and analogous trends predicted for properties such as vibrational frequency shifts and vibrational inelasticit...

Anisotropic intermolecular forces

Anisotropic potential energy surfaces for Ne·HCl, Kr·HCl and Xe·HCl are obtained by simultaneous least squares fitting to molecular beam spectra and rotational line broadening cross sections. A revised potential surface for Ar·HCl is also presented. The potentials are all very similar in shape, with the absolute minimum at the linear rare gas—HCl geometry in each case. The absolute well depths and well depth anisotropies increase steadily as the size of the rare gas atom increases. The potentials should be reliable in the region of the absolute minimum and on the repulsive wall of the potential. The molecular beam spectra for Ne·HCl can be fitted only by a potential with a significant secondary minimum at the linear Ne·Cl-H geometry, but the existing data for the more anisotropic Ar, Kr and Xe systems are not sensitive to the presence of this potential feature. The potential surfaces for these systems have accordingly been constrained to have a similar secondary minimum near the linear rare gas-ClH geomet...

The dynamics of open-shell Van der Waals complexes

The theory of Van der Waals complexes formed from atoms and open‐shell (Σ and Π) diatomic molecules is developed, paying particular attention to the quantum numbers that are conserved in the complex and the angular momentum coupling cases that may be observed. Complexes formed from diatoms in multiplet Σ states may exhibit several different coupling schemes closely analogous to Hund’s coupling cases for diatomic molecules. Complexes formed from diatoms in Π states usually exhibit a coupling scheme in which the (signed) projection P of the diatom angular momentum j onto the intermolecular axis is nearly conserved. Correlation diagrams showing the bending energy levels as a function of potential anisotropy are given for complexes containing diatomic molecules in both Σ and Π states. The transition from free internal rotor quantum numbers to near‐rigid bender quantum numbers with increasing anisotropy is investigated. The cases of Ar–OH and Ne–OH are considered as examples.

Centrifugal distortion constants for diatomic molecules: an improved computational method

The perturbation theory approach to calculating centrifugal distortion constants is reformulated to eliminate summations over excited vibrational states. In the usual formulation of Rayleigh-Schrodinger perturbation theory, these summations appear when the solution of an inhomogeneous differential equation is expressed as a sum over the eigenfunctions of the unperturbed Hamiltonian. In the present method, this differential equation is solved numerically, eliminating the summations and giving an exact solution using much less computer time than in the original perturbation theory method. The centrifugal distortion constants are then calculated by a straightforward numerical integration. The effects of continuum levels are included exactly, so that the results remain valid for vibrational levels near dissociation. Numerical tests are performed for realistic potential curves, and the method is shown to give accurate results.

The intermolecular potential energy surface of Ar · HC1

Anisotropic potential energy surfaces for Ar · HC1 are obtained by simultaneous least squares fitting to molecular beam spectra, rotational line broadening cross sections, second virial coefficients and molecular beam total differential cross sections. Several potentials are obtained which given good agreement with all these data and the sensitivity of the data to various aspects of the potential is investigated. For all potentials the equilibrium configuration is linear with the atomic arrangement Ar · H-C1. Several different ways of parameterizing the intermolecular potential are considered and it is concluded that the conventional multipole parameterization is not adequate for strongly anisotropic intermolecular potentials.

An ultracold high-density sample of rovibronic ground-state molecules in an optical lattice

Control over all internal and external degrees of freedom of molecules at the level of single quantum states will enable a series of fundamental studies in physics and chemistry(1,2). In particular, samples of ground-state molecules at ultralow temperatures and high number densities will facilitate new quantum-gas studies(3) and future applications in quantum information science(4). However, high phase-space densities for molecular samples are not readily attainable because efficient cooling techniques such as laser cooling are lacking. Here we produce an ultracold and dense sample of molecules in a single hyperfine level of the rovibronic ground state with each molecule individually trapped in the motional ground state of an optical lattice well. Starting from a zero-temperature atomic Mott-insulator state(5) with optimized double-site occupancy(6), weakly bound dimer molecules are efficiently associated on a Feshbach resonance(7) and subsequently transferred to the rovibronic ground state by a stimulated four-photon process with >50% efficiency. The molecules are trapped in the lattice and have a lifetime of 8 s. Our results present a crucial step towards Bose-Einstein condensation of ground-state molecules and, when suitably generalized to polar heteronuclear molecules, the realization of dipolar quantum-gas phases in optical lattices(8-10).

Anisotropic intermolecular forces: II. Rare gas-hydrogen fluoride systems

Anisotropic intermolecular potentials for Ar · HF, Kr · HF and Xe · HF are obtained by least squares fitting to molecular beam spectra of van der Waals complexes. The absolute minimum is at the lin...

Rotational predissociation of the Ar⋅HCl van der Waals complex: Close‐coupled scattering calculations

We report an extensive computational study of rotationally predissociating metastable states of the Ar⋅HCl van der Waals complex, using a highly realistic empirical intermolecular potential recently proposed by Hutson and Howard. The states are characterized by fully converged, close‐coupled, scattering calculations. Resonance energies, widths, and partial widths are extracted by fitting the energy dependence of S matrices. Total angular momenta of 0 and 1 are studied, and the calculations span an energy range from 0 to 1400 cm−1. The resonance widths vary from <10−4 to ≳5 cm−1, and it is shown that the isolated narrow resonance approximation is of poor validity for the wider resonances. Comparison of the close‐coupling results with approximate calculations enables assignment of approximate quantum numbers to the metastable states. Physical explanations are suggested for the strong trends in resonance parameters as a function of the intermolecular stretching, diatom rotation, and molecule‐fixed angular mo...

Ultracold dense samples of dipolar RbCs molecules in the rovibrational and hyperfine ground state.

We produce ultracold dense trapped samples of ^{87}Rb^{133}Cs molecules in their rovibrational ground state, with full nuclear hyperfine state control, by stimulated Raman adiabatic passage (STIRAP) with efficiencies of 90%. We observe the onset of hyperfine-changing collisions when the magnetic field is ramped so that the molecules are no longer in the hyperfine ground state. A strong quadratic shift of the transition frequencies as a function of applied electric field shows the strongly dipolar character of the RbCs ground-state molecule. Our results open up the prospect of realizing stable bosonic dipolar quantum gases with ultracold molecules.