John R. Ferraro

The infrared spectrum of ammonia hydrate: Explanation for a reported ammonia phase

A number of anomalous spectra of solid NH3 deposited from the vapor phase have appeared in the literature. These spectra have been ascribed to a new phase of NH3. In the experiment reported here these anomalous spectra were reproduced by depositing a thin film from a mixture of gaseous NH3 and H2O and annealing this film at a temperature of 162 °K. The thin film spectra showed excellent agreement with recent data on NH3⋅H2O. The anomalous ’’NH3’’ spectra are, therefore, seen to be caused by H2O contamination of solid NH3 with formation of NH3 hydrate.

FT-IR Micro-Spectroscopic Studies of Several Charge-Transfer Organic Electrical Conductors:

A series of infrared reflectance measurements using FT-IR Micro methods were conducted on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or “ET”) and bis(propylenedithio)tetrathiafulvalene (BPDT or “PT”) salts of the type (ET)2X, where X = I3, AuCl2−, AuBr2−, AuI2−, I2Br−, IBr2, ICl2, ReO4−, ClO4−, and ; and (PT)2X, where X = I3−, IBr2−, I2Br−, and ICl2−. The technique is useful for characterizing, at room temperature, differences between β-, β′- and α′-type structures vs. α-structures. The β-, β′-, and α′-type structures show a vibrational feature at ∼1280 cm−1 which has been assigned as the -C-C-H bending vibration and is absent in the spectrum of the α-type salts. This vibration shifts toward higher frequency in going from the PT to the ET salts, and the results indicate stronger hydrogen bonding and harder lattices in the ET salts as opposed to the PT salts. This frequency shift also appears to be a function of the electronegativity of the halogen in the anion moiety of the charge-transfer salt.

Diffuse Reflectance Interferometric Spectroscopy in the Far Infrared Region

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy in the far infrared (FIR) has been found to be feasible to ∼40 cm−1. High-density polyethylene powder was used as the non-absorbing matrix and diluent. DRIFT spectra in the FIR of compounds representing organic, inorganic, corrdination, glass, catalysts, and others are presented, and are compared with Nujol mull transmission spectra. Other sampling techniques are suggested, including specular (external reflectance—1 pass) reflectance in the FIR.

Reststrahlen Effects in Drift Experiments of Alkali Metal Halides in the Far-Infrared Region

DRIFT experiments in the far-infrared region are new. In the course of developing this technique, we have obtained some unusual results with the alkali metal halides due to the reststrahlen phenomenon. Neat solids (powder, single crystal, pressed pellets), as well as matrix (powdered polyethylene) diluted salts, gave inverse peaks (maxima in intensity on a percent T plot and a minima on an absorbance plot). The use of the blocker device on the diffuse reflectance attachment failed to normalize the peaks. The inverted peaks centered in the vTO and vLO phonon regions, with the intensity relation being vTO > vLO. The inverse mode at the low-frequency region near the vTO mode was found always at higher energy than the vTO mode obtained by thin film experiments. It also was accompanied by shoulders on the high- and low-frequency sides. The weaker, higher frequency band was found to occur close to the vLO mode as determined by the Lyddane-Sachs-Teller equation. A Kramers-Kronig dispersion analysis was conducted and the changes in the index of refraction (n) and the absorption coefficient (K) were determined for various points around the dispersion frequency.

Molecular vibrational spectra of potassium peroxymonosulfate, KHSO5 and KHSO5 · H2O, and of the aqueous peroxymonosulfate ion☆

Both i.r. and Raman spectra of solid anhydrous KHSO5 and KHSO5 · H2O were measured, along with the Raman spectrum of the peroxymonosulfate ion, HSO−5, in aqueous solution. A normal coordinate analysis of the ion was carried out, and the fundamental frequencies and force constants are compared with those of the isoelectronic fluoroxysulfate ion, SO4F−.

Interfacing the DAC with an interferometer without a beam condenser

Since 1959, when the diamond anvil cell (DAC) was developed by researchers at the National Bureau of Standards, it has been possible to conveniently study materials at high pressures in the mid-infrared (MIR) region by infrared spectroscopy. The technique has subsequently been extended to the far-infrared (FIR) region, and at present, applications of the DAC extend from the edge of the ultraviolet region to the far-infrared. Because of its compact size, the DAC can readily fit into the sample compartment of a variety of infrared spectrophotometers (dispersive and interferometric), and a number of unique investigations have been possible. Further, with the advent of the laser, Raman scattering experiments at high pressures also became possible with the DAC. Recently, an advanced generation of the DAC called the ultra-high-pressure DAC has been used in visible and Raman studies into the megabar region.

The Use of the Infrared-Active AgI Phonon Mode in AgI-type Ionic Conductors to Study Order-Disorder Phenomena

Several new ionic conductors of the type RHI·AgI, where R = substituted pyridinium group, were recently synthesized. Conductivity studies made at high pressures demonstrated diverse responses in the ionic conductivity. Some conductors showed a maxima in ionic conductivity, while others manifested a decrease or were unresponsive to the application of pressure. These changes in conductivity were found to occur without any noticeable phase transitions, as determined by visual microscopic observation, and presumably involve only subtle lattice modifications. It has been suggested that these pressure-induced modifications in the lattice could cause redistributions in the population of different Ag ion sites, and provide more facile ion transport with consequent increased conductivity. The importance of such lattice modifications as one of the criteria for increased conductivity has been cited for related ionic conductors.

Vibrational Studies of 13C- and 34S-Labeled Bis(Ethylenedithio)Tetrathiafulvalene (ET) Donor Molecule

FT-IR and FT-Raman studies of 13C- and 34S-labeled bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) electron-donor molecules were made, and the results are presented. Assignments for fundamental vibrations in ET were verified. Spectral data suggest that ET has no center of symmetry (confirming X-ray data) and that the data can be reconciled by a D-type point group with only slight interactions occurring between the four molecules per unit cell.

Reststrahlen Effects in Drift Experiments for NaCl in the Far-Infrared Region

The alkali metal halides possess the NaCl structure under ambient conditions of temperature and pressure (O h 5 , Fm3m with Z = 1). No activity is observed in the first-order Raman spectrum, but an F1u mode (triply degenerate) is observed in the far infrared region.

An Overview of Techniques Used in FT-IR Spectroscopy

The advent of commercial Fourier transform interferometry (FT-IR) instrumentation has provided the materials scientist, the analytical chemist, the research scientist and others, with another tool to solve their problems. It is our intention in this paper to present an overview of the techniques that can be used in FT-IR, and can be directed toward materials characterization.