15min:

HUI LI AND ROBERT J. LE ROY, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; NICHOLAS BLINOV AND PIERRE-NICHOLAS ROY, Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.

High resolution infrared spectra of (He)_N-CO₂ clusters with N up to 60 have been studied by McKellar and co-workers, in the region of the ₃ fundamental band of CO₂.\footnote J. Tang et al. Phys. Rev. Lett. 92, 145503 (2004); ~A.R.W. McKellar, J. Chem. Phys. 128, 044308 (2008).~ By fitting to the rotation-vibration transitions for each cluster size, vibrational band origins ₀ and rotational constants B and D were obtained as functions of N. Quantum Monte Carlo simulation predictions of B and D for (He)_N-CO₂ clusters have been found to agree well with experiment for N values up to 17.\footnote F. Paesani, Y. Kwon and K.B. Whaley Phys. Rev. Lett. 94, 153401 (2005); ~N. Blinov and P.-N. Roy J. Low Temp. Phys. 140, 314 (2005); ~F. Mezzacapo, J. Low Temp. Phys. 140, 241 (2005).~ However, those simulations were based on two-dimensional potential energy surfaces with CO₂ fixed at its equilibrium geometry. While an adequate approximation for describing rotational constants, that approach cannot predict the ₃ vibrational band origin shift of CO₂ in (He)_N clusters, because of neglect of the dependence of the potential energy surface on the Q₃ asymmetric-stretch motion of CO₂.

We recently determined a three-dimensional analytical `Morse/Long-Range' potential energy surface for the CO₂-He bimer, which explicitly depends on the Q₃ asymmetric-stretch vibrational motion of CO₂, and also incorporates the correct angle-dependent inverse-power long-range behaviour.~ We have used this new potential in path-integral Monte Carlo simulations to predict both the effective rotational constant and the shift of the ₃ band origin for CO₂ doped in (He)_N clusters with N up to 100. Our results will be compared with experiment for clusters formed from both symmetric and asymmetric isotopologues of CO₂.