A NEW POTENTIAL ENERGY SURFACE FOR N$_2$O--He, AND PIMC SIMULATIONS PROBING INFRARED SPECTRA AND SUPERFLUIDITY

Abstract

High resolution infrared spectra of an N$_2$O molecule seeded in ultra-cold helium custers have been reported by two groups.\ {\bf 91}, 163401 (2003).}$^,$\ {\bf 127}, 044315 (2007).}~ Early simulations of N$_2$O--(He)$_n$ clusters\ {\bf 121}, 3577 (2004).}$^,$\ {\bf 121}, 5293 (2004).} were performed using potential energy surfaces (PESs) for which the dopant N$_2$O molecule was frozen at its equilibrium geometry. Since the evolution of the shift of the $\nu_3$ band-origin of N$_2$O provides a key link to bridge the gap between micro and macro world, a new 3D PES was generated which incorporated the asymmetric-stretch $Q_3$ vibrational motion of the N$_2$O.\ {\bf 124}, 144317(2006).}~ Bosonic PIMC simulations\ {\bf 130}, 144305(2009).} based on this surface were then used to study rotational dynamics, and energetic and superfluid properties of N$_2$O--(He)$_n$ clusters. The evolution of the calculated shifts agree reasonably with the experimental results, but some quantitative discrepancies remain. To address this problem, a new four-dimensional N$_2$O--He PES has now been obtained which also takes account of the change in the average value of the $Q_1$ symmetric-stretch coordinate on excitation of $\nu_3$. It has been fitted to a generalized MLR functional form\ {\bf 10}, 04128 (2008).} which imposes better long-range behaviour. Results obtained using this new surface will be presented.