The rotational spectrum of single OCS molecules in liquid 4He droplets

Abstract

Single OCS molecules have been embedded in large 4He droplets (N̄=1×103–8×103 atoms) and their infrared spectra in the vicinity of the ν3-fundamental at 2062 cm−1 have been studied using coaxial laser depletion spectroscopy. Sharp lines corresponding to the P- and R-branches with a linewidth of 160 MHz or greater are observed. From the line intensities a droplet temperature of 0.37±0.02 K is obtained and from the line positions the rotational constants B for the ground and excited states and an average centrifugal distortion constant D are determined. The former are about a factor of 2.8 smaller and the latter four orders-of-magnitude larger than for the free molecule. The decrease in B is attributed to an attached nonsuperfluid component which has the same effect as a ring of about six 4He atoms in an equatorial plane around the waist of the OCS molecule, which is carried along in the end-over-end rotation. The widths of the individual lines show an interesting asymmetry which is oppositely sloped for the P- and R-branches and increases with the rotational quantum number. Several possible explanations for the line shapes and widths are presented.

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

“…The resulting value was found to be B eff = 0.084± 0.004 cm −1 , which is in reasonable agreement with the experimental value of the nanodroplet B eff = 0.0732 cm −1 . 56 An effective moment of inertia I eff defined by B eff ϵ ប 2 /2I eff was estimated to be 201± 11 amu Å 2 , which is comparable with the experimental value for the nanodroplet, I eff = 230 amu Å 2 . 56 The small ͑but non-negligible͒ discrepancy between the present calculation and the experimental nanodroplet value will be discussed in the companion paper II.…”

“…56 An effective moment of inertia I eff defined by B eff ϵ ប 2 /2I eff was estimated to be 201± 11 amu Å 2 , which is comparable with the experimental value for the nanodroplet, I eff = 230 amu Å 2 . 56 The small ͑but non-negligible͒ discrepancy between the present calculation and the experimental nanodroplet value will be discussed in the companion paper II. 12 In Fig.…”

RETRACTED ARTICLE: Quantum effects on translation and rotation of molecular chlorine in solid para-hydrogen

“…This has been observed, e.g., for the CO@Ar cryogenic system for which a pseudorotating cage model was developed, thus explaining the increased moment of inertia and hence the reduced rotational constant [58]. In extreme cases, such as OCS molecules in liquid 4 He clusters, the effective moment of inertia is more than doubled [59]. However, in the present case of Cl 2 @pH 2 , even by taking the largest displacement found in our simulations, the increase in the moment of inertia due to pseudorotation is still less than 1% because of the light mass of molecular hydrogen easily following the Cl 2 rotations, so that the rotational spectrum is not expected to show notable effects of pseudorotation.…”

Structure and Spectroscopy of Doped Helium Clusters Using Quantum Monte Carlo Techniques

“…The increase of the moment of inertia measured in helium droplets 18 leads to a ratio B/B 0 ∼ 37 % that is nevertheless similar to the ratio for SF 6 . Because the anisotropy of the OCS-He potential 20 is very pronounced, we expect that adiabatic following will also be strong for this system, even though the rotor is somewhat faster than SF 6 .…”