Phase Separation in Cold Para-H_{2} D_{2} Clusters.

Low temperature phase separation in mixtures of ^{3}He and ^{4}He isotopes is a unique property of quantum fluids. Hydrogen has long been considered as another potential quantum liquid and has been predicted to be superfluid at T≤1  K, well below freezing temperature of ≈14  K. Phase separation has also been predicted in mixtures of para-H_{2} and D_{2} at temperatures ≤3  K.

Ro-vibrational Spectra of (para-H ) -CH in He Droplets.

In this work, we report on the infrared spectroscopic study of clusters of CH molecules with up to N=80 para-hydrogen molecules assembled inside He droplets. Upon increase of the number of the added para-hydrogen molecules up to about N=12, both the rotational constant, B, and the origin frequency of the υ band of CH decrease gradually. In the range of 6 ≤N≤12, the spectra indicate some abrupt changes of B and υ with both values being approximately constant at N≥12.

Infrared spectra in the 3 μm region of ethane and ethane clusters in helium droplets.

Ethane and ethane clusters (N ≈ 10(2)-10(4)) were studied inside helium droplets with infrared laser spectroscopy. The spectra were measured in the 2880-3000 cm(-1) range, which covers the ν5, ν(8+11), and ν7 vibrational bands of ethane. Partially resolved rotational fine structure in the spectrum of the monomer reveals solvent-induced band origin blue shifts that are each approximately 1 cm(-1).

Sizes of large He droplets.

Helium droplets spanning a wide size range, N(He) = 10(3)-10(10), were formed in a continuous-nozzle beam expansion at different nozzle temperatures and a constant stagnation pressure of 20 bars. The average sizes of the droplets have been obtained by attenuation of the droplet beam through collisions with argon and helium gases at room temperature. The results obtained are in good agreement with previous measurements in the size range N(He) = 10(5)-10(7).

Fast nuclear spin conversion in water clusters and ices: a matrix isolation study.

Single water molecules have been isolated in solid Ar matrices at 4 K and studied by rovibrational spectroscopy using FTIR in the regions of the ν(1), ν(2), and ν(3) modes. Upon nuclear spin conversion at 4 K, essentially pure para-H(2)O was prepared, followed by subsequent fast annealing generating ice particles. FTIR studies of the vapor above the condensed water upon annealing to T ≥ 250 K indicate fast reconversion of nuclear spin to equilibrium conditions.

Temperature dependence of the Raman spectra of liquid parahydrogen.

Vibrational and rotational spectra of liquid para-H(2) at temperature T=14-26 K and of solid at T=6-13 K have been obtained using coherent anti-Stokes Raman scattering technique. The vibrational frequency in the liquid increases with temperature by about 2 cm(-1) and the shift scales with the square of the sample's density. An extrapolation of the vibrational frequency in the metastable para-H(2) liquid below the freezing point is discussed.

Interchange-tunneling splitting in HCl dimer in helium nanodroplets.

Midinfrared spectra of HCl dimers have been obtained in helium nanodroplets. The interchange-tunneling (IT) splitting in the vibrationally excited state of the bonded H-Cl stretching band (nu(2)) in (H(35)Cl-H(37)Cl) dimers was measured to be 2.7+/-0.