The rotational dynamics of N2-HF and OC-HF in helium nanodroplets

Infrared spectra are reported for the N-2-HF and OC-HF complexes formed in helium nanodroplets. The spectra are rotationally resolved and show that the structures of the complexes are essentially the same (linear) as determined previously from gas phase studies. The rotational constants of the helium solvated complexes are smaller than the gas phase values, in agreement with what has been previously observed for several other systems. N-2-HF is particularly interesting when studied in the presence of a large electric field, given that the change in the dipole moment upon vibrational excitation is large, so that the individual transitions in the pendular spectrum can be resolved. This enables us to monitor the change in the helium environment around the molecule as it goes from rotational to pendular motion. The results also reveal that the relaxation lifetime of these pendular states in helium is comparable to the flight time of the droplets through the electric field and depends upon the droplet size. (C) 2002 American Institute of Physics.