Cold collisions of heavy 2Σ^2\Sigma molecules with alkali-metal atoms in a magnetic field: Ab initio analysis and prospects for sympathetic cooling of SrOH(2Σ)(^2\Sigma) by Li(2^2S)

We use accurate ab initio and quantum scattering calculations to explore the prospects for sympathetic cooling of the heavy molecular radical SrOH($^2\Sigma$) by ultracold Li atoms in a magnetic trap. A two-dimensional potential energy surface (PES) for the triplet electronic state of Li-SrOH is calculated ab initio using the partially spin-restricted coupled cluster method with single, double and perturbative triple excitations and a large correlation-consistent basis set. The highly anisotropic PES has a deep global minimum in the skewed Li-HOSr geometry with $D_e=4932$ cm$^{-1}$ and saddle points in collinear configurations. Our quantum scattering calculations predict low spin relaxation rates in fully spin-polarized Li+SrOH collisions with the ratios of elastic to inelastic collision rates well in excess of 100 over a wide range of magnetic fields (1-1000 G) and collision energies (10$^{-5}-0.1$~K) suggesting favorable prospects for sympathetic cooling of SrOH molecules with spin-polarized Li atoms in a magnetic trap. We find that spin relaxation in Li+SrOH collisions occurs via a direct mechanism mediated by the magnetic dipole-dipole interaction between the electron spins of Li and SrOH, and that the indirect (spin-rotation) mechanism is strongly suppressed. The upper limit to the Li+SrOH reaction rate coefficient calculated for the singlet PES using adiabatic capture theory is found to decrease from $4\times 10^{-10}$~cm$^3$/s to a limiting value of $3.5\times 10^{-10}$ cm$^3$/s with decreasing temperature from 0.1 K to 1 $\mu$K

Electronic and vibrational predissociation in Ari2 photodissociation dynamics

A quantum dynamical study of the ArI2 predissociation where both vibrational and electronic processes can take place was performed. A set of 5 coupled diatomics-in-molecules (DIM) electronic potentials was used. Both perpendicular and linear initial ArI2(X) isomers were considered. Only the a′ state had non-negligible effect on photodissociation dynamics for the linear isomer. Decay rates oscillated as a function of the vibrational excitation of I2(B) but the intramolecular vibrational energy was the main source of energy which occurred in vibrational predissociation.This work has been supported by DGICYT @Ministerio de Educacio´n y Ciencia ~MEC!, Spain# under Grant No. PB95-0071, INTAS under Grant No. 97-31573, and the Spanish–French PICASSO Project No. HF1999-0132. A.A.B. also thanks MEC for sabbatical fellowship.Peer Reviewe

ArI2(X)→Ar+I2(B) photodissociation: Comparison between linear and T-shaped isomers dynamics

An attempt was made to compute the spectra and product state distributions on semiempirical and ab initio electronic potential energy surfaces for both linear and T-shaped ArI2(X) isomers. It was shown that whereas the T-shaped isomer dynamics is dominated by resonances, dissociation of the linear isomer involves competition between a fast direct process and slower vibrational predissociation of near-linear resonances.This work has been supported by DGICYT @Ministerio de Educación y Ciencia (MEC), Spain, under Grant No. PB95- 0071, INTAS under Grant No. 97-31573 and the SpanishFrench PICASSO project No. HF1999-0132. One of authors (A.A.B) also thanks MEC for sabbatical fellowship.Peer Reviewe

Weakly bound molecules as sensors of new gravitylike forces

Several extensions to the Standard Model of particle physics, including light dark matter candidates and unification theories predict deviations from Newton’s law of gravitation. For macroscopic distances, the inverse-square law of gravitation is well confirmed by astrophysical observations and laboratory experiments. At micrometer and shorter length scales, however, even the state-of-the-art constraints on deviations from gravitational interaction, whether provided by neutron scattering or precise measurements of forces between macroscopic bodies, are currently many orders of magnitude larger than gravity itself. Here we show that precision spectroscopy of weakly bound molecules can be used to constrain non-Newtonian interactions between atoms. A proof-of-principle demonstration using recent data from photoassociation spectroscopy of weakly bound Yb2 molecules yields constraints on these new interactions that are already close to state-of-the-art neutron scattering experiments. At the same time, with the development of the recently proposed optical molecular clocks, the neutron scattering constraints could be surpassed by at least two orders of magnitude

Competition between adiabatic and nonadiabatic fragmentation pathways in the unimolecular decay of the ArI2(B) van der Waals complex

12 pages, 6 figures, 3 tables, 1 appendix.-- PACS nrs.: 34.50.Ez; 33.80.Gj; 33.70.Ca; 33.15.Mt; 31.15.Md; 33.20.Tp.The competition between vibrational and electronic predissociations of the ArI2(B) van der Waals complex has been studied using several dynamical computational methods: exact quantum wave-packet propagation, time-dependent golden rule, and quasiclassical trajectory with quantum jumps model. Five electronic states are considered using recent three-dimensional coupled surfaces obtained with a perturbative diatoms-in-molecules method. Final vibrational and electronic populations, predissociation rates, and absorption spectra have been computed for I2(B,ν = 18–24) <-- I2(X,ν = 0) excitations within the complex. The contribution of vibrational predissociation into the total decay oscillates as a function of vibrational excitation due to intramolecular vibrational relaxation in a sparse-intermediate regime, which induces irregular variations of the total decay rate. Franck–Condon oscillations control the branching ratios of the individual electronic predissociation channels. However, since these oscillations are out of phase as a function of vibrational excitation, they have limited effect on the oscillatory behavior of the total predissociation rate. Comparison between exact quantum and perturbative golden rule calculations shows that vibrational predissociation has some impact on the electronic predissociation process and affects the final electronic distributions. On the contrary, vibrational product distributions are not significantly affected by the electronic predissociation. A classical description of the ArI2 dynamics provides an averaged picture of the competing predissociation processes, being better adapted for treating intermolecular vibrational relaxation in the statistical limit.An allocation of CPU time on the NEC SX-5 vector computer of the "Institut du Développement et des Ressources Informatiques Scientifiques" is gratefully acknowledged. The authors also wish to acknowledge a CNRS-CSIC, Grant No. 2004FR0003, for supporting travel expenses between Toulouse and Madrid. A.A.B. acknowledges Paul Sabatier University for Invited Professor fellowship and Russian Fund of Fundamental Research for financial support (Project No. 02-03-32676). O.R. thanks Ministerio de Ciencia y Tecnología, Spain, for financial support under Grant No. BFM2001-2179.Peer reviewe