Spectra of the ν1 and ν3 bands of water molecules in helium droplets

Depletion spectra of the ν1 and ν3 ro-vibrational bands of water molecules embedded in He droplets have been studied in the range of ν = 3600–3900 cm−1. The effective rotational constant of water in helium (BHe + CHe)/2 was found to be about 3% smaller than that of free H2O. Vibrational relaxation time of the ν3 state in He was estimated from the laser power saturation dependence of the depletion signal to be about or longer than 7 × 10−9 s. Rotational relaxation time of different levels in the ν1 and ν3 states was estimated from the line widths to be about 2 × 10−12 s. Fast rotational relaxation was ascribed to the creation of short wavelength roton collective excitations in the He droplets.