Far-Infrared Dielectric Properties of Polar Liquids Probed by Femtosecond Terahertz Pulse Spectroscopy

We report the frequency-dependent optical constants, n(ν) and α(ν), or, equivalently, the complex permittivity ε(ω) = ε‘(ω) − iε‘‘(ω), over the frequency range from 2 to 50 cm-1 for water, methanol, ethanol, 1-propanol, and liquid ammonia. These spectra have been measured with femtosecond terahertz pulse transmission spectroscopy. These liquids exhibit multiple-Debye behavior, making their frequency-dependent dielectric constants valuable benchmarks for molecular dynamics simulations and other theoretical treatments of liquids.