Terahertz and infrared spectroscopy of hydrogen-bonded clusters in ultrahigh vacuum

Yamakawa, Koichiro   ; Nasu, Hirokazu*; Suzuki, Natsumi*; Shimizu, Genki*; Arakawa, Ichiro*

Nano-sized molecular clusters have been intensively investigated in a spectroscopic way to reveal the nature of intermolecular interaction. Compared with the infrared (IR) range, only a few spectral measurements in the terahertz (THz) range have been reported, so that the assignment of the vibrational mode to THz absorption was not established even for the water dimer. In the present study, we constructed an experimental apparatus for THz-IR absorption spectroscopy in an ultrahigh vacuum and measured spectra of deuterated-water clusters formed in solid Ar to identify the THz absorption peaks of the dimer, trimer, and tetramer.