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

Abstract

We report the frequency-dependent optical constants, n(ν) and R(ν), or, equivalently, the complex permittivity ˆ(ω) ) ′(ω)i ′′(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.

Dielectric properties of liquid ethanol. A computer simulation study

“…In the case of alcohols, only the dielectric properties of liquid methanol [2][3][4] and methanol-water mixtures 5 have been analyzed by computer simulation. Many experimental studies of both static and dynamic dielectric properties of hydrogen bonded liquids have been carried out, but in the case of ethanol, the latter are restricted to the microwave region of the spectra 6 and to the infrared region 7 up to about 34 cm Ϫ1 . To achieve a better understanding of the dielectric properties of monohydric alcohols, we show in this article the results obtained for liquid ethanol by means of MD simulations.…”

Uncertainty and Ambiguity in Terahertz Parameter Extraction and Data Analysis

“…This can be improved when multiple sample thickness d have been probed. In this case, n s is fitted to the phase ϕ(d) and α s is fitted to ln(δ * δ ) [3].…”

“…The imaginary part ε ′′ describes the damping of the wave.ε can be fit to different multi-modal relaxation models, which is a well-known method [3,30].…”

“…Developed in the 1980s and 1990s [1,2], THz time-domain spectroscopy (THz TDS) has been established as a general spectroscopic technique to study liquids [3], solids [4], gases [5], biomolecules [6,7], aqueous salt solutions [8], nanoparticles [9], semiconductors [10] and plasmas [11]. The covered frequency bandwidth ranges from 3 cm −1 to 140 cm −1 (0.1 THz to 4 THz).…”

“…Using implicit function theorem, a rigourous error propagation as well as a simplified model are presented. This paper focuses on the analysis of TDS spectra in transmission geometry [3], although the conclusions are transferable to other geometries such as reflection [25], ellipsometry [26], interferometry [27] or differential TDS [28].…”