Spectroscopic Studies of Quantum Solvation inHeN4−N2OCl

Abstract

High resolution microwave and infrared spectra of He(N)-N2O clusters were studied in the range N=3 to 12. The apparent cluster moments of inertia increase from N=3 to 6, but then decrease, showing oscillatory behavior for N=7 to 12. This provides direct experimental evidence for the decoupling of helium atoms from the rotation of the dopant molecule in this size regime, signaling the transition from a molecular complex to a quantum solvated system and directly exploring the microscopic evolution of "molecular superfluidity."

Bridging the Gap between Small Clusters and Nanodroplets: Spectroscopic Study and Computer Simulation of Carbon Dioxide Solvated with Helium Atoms

“…Quantum Monte Carlo (QMC) calculations of rotational excitations of the cluster confirm the observed undershoot, locating the minimum of B at N = 6 [14] or 8-9 [15]. Experimentally, such a turnaround has been observed in 4 He N -N 2 O, with a first minimum of B at N = 6, followed by an oscillatory behavior [11]. For N 2 O, however, the value of B obtained for all clusters for N up to 12 is significantly above its nanodroplet limit [12].…”

“…For He N -OCS, B decreases steadily from N = 0 to 8, passing through the nanodroplet value at about N = 5, and its eventual turnaround has not yet been observed experimentally [10]. For He N -N 2 O, the variation of B is rather similar to that of He N -CO 2 , but with the significant difference that B always remains above its nanodroplet value for He N -N 2 O [11]. The He N -CO 2 and He N -N 2 O rotational parameters are almost identical for N = 1, 3, 4, and 5.…”

“…Recently, measurements of the evolution of rotational constants with the size of the cluster have been reported [10,11]. For 4 He N -OCS, B decreases in the range N < 8, undershooting its nanodroplet value, which implies a subsequent turnaround at larger cluster sizes [10].…”

“…1(b). Starting at the value for the isolated CO 2 molecule, 0.39 cm −1 , B drops to a minimum of 0.11 cm −1 at N = 5, and then rises through a broad local maximum of 0.20 cm −1 around N = 11, signaling a transition to a regime where a fraction of the helium density is decoupled from the rotation of the molecule [11,14,15]. For N = 14 to 17, B decreases slightly to an almost constant value of 0.18 cm −1 .…”

Rotational fluctuation of molecules in quantum clusters. I. Path integral hybrid Monte Carlo algorithm

“…1,2 While the spectroscopic measurements have been carried out using the nanodroplets consisting of several thousand atoms, recent experimental advances allow the study of clusters containing one to about 20 helium-4 atoms, showing the size dependence on the molecular motion doped in the clusters. [6][7][8][9][10] Very recent spectroscopic study on the doped helium clusters reveals rich size dependence of the dopant rotational fluctuation in the size up to N = 72. 11 In this paper ͑paper I͒ and a companion paper ͑paper II͒, 12 molecular fluctuations of the dopants in the helium-4 cluster are studied in detail using a path integral simulation technique.…”