A review is presented of recent developments in the methods of dispersive Fourier transform spectroscopy that have demonstrated the unique value of this broad band method for determining the optical constants of gases, liquids and solids.

Dispersive Fourier Transform Spectroscopy

Far-infrared absorption spectra of liquid acetonitrile at temperatures ranging from 238 to 343 K were measured with a source of synchrotron orbital radiation. On the basis of an optical theory, a theoretical expression for transmittance of a cell filled with liquid was obtained as a function of the optical constants of the liquid. Assuming an analytical form with seven parameters for the absorption coefficients, the refractive indices were analytically calculated by the Kramers-Kronig relation. The parameters of the absorption coefficients were adjusted by least-squares fitting of the theoretical transmittance to the observed transmittance. The resulting optical constants at 298 K were in good agreement with the previously reported results by a laser ATR method. The effect of temperature on the band shape of the absorption is remarkable and will provide an important clue to molecular reorientational dynamics. On the other hand, the molecular dipole moments obtained from the integrated intensities are near...

Far-infrared optical constants of liquid acetonitrile at 238 to 343 K as measured with a synchrotron radiation source

In this review, the contribution of spin chemistry (in particular, magnetic resonance-related chemistry) to the photochemical field is briefly introduced. First, the development of a time-resolved EPR method and its significant application to radical-related physical phenomena and chemical reactions are presented. Second, a reaction-control method by means of electron spin operations is introduced, and several reaction yield-detected magnetic resonance (RYDMR) methods are presented as applications of this concept. One of the most important physical conclusions is the introduction of the concept of “spin phase relaxation” termed singlet–triplet ( S – T ) and triplet–triplet ( T – T ) dephasing, instead of the traditional concepts of longitudinal ( T 1 ) and transversal relaxations ( T 2 ). The effects of strong microwave power on the RYDMR spectrum and time-domain data are analyzed according to this concept. Furthermore, a new detection method is introduced, termed “photoconductivity detected magnetic resonance” (PCDMR), which is applicable exclusively to the system of charge transfer reactions.

Spin-chemical approach to photochemistry: reaction control by spin quantum operation

The study of enzymatic protein molecules using terahertz time-domain spectroscopy (THz-TDS) has the potential to reveal molecular activity in real time without the use of labelling. Molecular hydration, or bound water, is a critical parameter in enzyme activity and THz-TDS measurements. For the first time we experimentally measure the terahertz-frequency response of nano-sized particles of protein and their level of molecular hydration. These measurements are valuable in understanding the terahertz response of biological systems and in studying the interaction between bound water and proteins.

Terahertz spectroscopy of bound water in nano suspensions

The wavelength, polarization, and output power of several lines of the optically pumped CW FIR12CH 3 16OH (methanol) and12CH 3 16OD (1-D deuterated methanol), methyl iodide, methyl bromide, and deuterated methylene chloride lasers have been determined. In addition to lines already reported in the literature, seven strong lines have been observed. Optimum performance of the laser system is achieved by means of an improved coupling of the CO 2 pump power into the resonator and extraction of the FIR power from the resonator. Measurements on the power absorption coefficient of water using the laser indicate that \alpha(\bar{\nu}) rises to almost 1100 Np ċ cm-1at 170 cm-1, and then shows a gradual fall with an increase in frequency. A strong temperature dependence of the 200 cm-1peak in \alpha(\bar{\nu}) is predicted, with a decrease in the frequency of maximum power absorption coefficient with an increase in temperature. The range of measurements for acetonitrile is extended to lower frequencies so as to overlap with those determined from other millimeter wave techniques. For highly power-absorbing liquids, \alpha(\bar{\nu}) is estimated to be within ± 5 percent.

Some new FIR laser lines of optically pumped 12 CH 3 16 OH, 12 CH 3 16 OD, and 12 CH 3 I, 12 CH 3 Br, 12 CD 2 Cl 2 absorption spectroscopy of water and acetonitrile

Kong Fan Ping

Papers

Upper bounds for discrete features in the far-infrared spectrum of liquid acetonitrile