James R. Scherer

Raman intensities of single crystal ice Ih

Raman intensities of single crystal H2O, D2O and HOD ice Ih were measured from −4 to −150°C. The cc, aa, ca, aa′ (c is the unique axis) polarizability components were measured from 20 to 4000 cm−1. Shoulders are observed on the high frequency side of the νOH and νOD bands of HOD which we attribute to combination bands between νOH and νOD and lattice modes. Intensities in the OH stretching region are interpreted using bond polarizability theory. The ratio of anistropy to mean polarizability for the OH bond was found to be 1.81. The analysis of the intensities suggests that those hydrogen bonds that statistically parallel to the c axis are slightly more linear than those that are equatorial to the c axis. The effects of intermolecular coupling of OH stretching vibrations are very evident in the spectra. However, it appears that such coupling is not the principal cause of the breadth of the isotropic part of the symmetric OH stretch band at −4°C. Evidence is presented that indicates extensive coupling of lib...

Effects of chain packing and chain mobility on the Raman spectra of biomembranes.

The degree of lateral crystal-like order between hydrocarbon chains in biomembrane systems can be estimated from Raman measurements in the C-H stretching region. Observations of the temperature dependence of the Raman spectra of crystalline n-C16H34 and the urea clathrate of n-C16H34 have enabled us to separate to some extent the overlapping effects of chain packing and chain mobility, effects that are normally not distinguished in considering lateral order. The mobility is associated with the freedom of an extended chain to rotate and twist about its long axis. A high degree of such motion must be ascribed to n-C16H34 in a urea clathrate in order to explain the unusual temperature behavior observed for Raman bands at 2885 and 1174 cm-1. Comparison of the temperature behavior of the Raman spectra of the clathrate with that of crystalline n-C16H34 permits the effects due to packing and to mobility to be distinguished. The same effects can be expected to be present in the Raman spectra of biomembranes.

A transferable force-field for out-of-plane vibrations of chlorinated benzenes

Abstract A twenty-three parameter force-field is found to reproduce 176 observed out-of-plane fundamentals of benzene and chlorinated benzenes to within 15 cm−1 with an average error of 3.5 cm−1. The force-constants which overlap the benzene molecule agree with the accepted Miller—Crawford values. The diagonal constants for CH bend and CCl bend decrease with substitution at adjacent ring positions and the CCCC torsion constant increases with substitution at the central CC bond. The values of o, m and p interaction constants between γCX (X  H, Cl) coordinates are found to deviate only slightly from those found for benzene. Inconsistencies were uncovered in the vibrational assignments of o-C6D4Cl2, C6D5Cl and 1,2,3,4-C6H2Cl4; certain fundamentals in these molecules are reassigned.

Raman spectra of liquid n‐alkanes. II. Longitudinal acoustic modes and the gauche–trans energy difference

Low‐frequency bands in the Raman spectra of the liquid n‐alkanes, n=9–20, have been identified with extended and certain nearly extended rotameric forms of these molecules. The bands are associated with the intense longitudinal‐acoustic‐mode (LAM‐1) band that appears in the Raman spectra of crystalline n‐alkanes. For liquids, the intensities of these bands are highly temperature dependent. This dependence was measured for the n=11–14 n‐alkanes and was used to determine an average value for ΔE, the energy difference between the trans and gauche states of the CC bond. The value determined for ΔE, 508±50 cal/mole, is very near the value commonly assumed in statistical calculations based on the rotational isomeric model. No evidence for local order was found even at temperatures just above the melting point of n‐C13H28 and n‐C14H30.

Raman spectra of liquid n‐alkanes. III. Energy difference between trans and gauchen‐butane

The energy difference between the trans and gauche forms of liquid n‐butane has been determined from the temperature dependence of Raman band intensities. A value of 557±13 cal/mole was derived from the summed integrated intensities of six bands of each rotamer measured at nine temperatures between 0 and −127 °C. This value is considerably lower than those determined earlier from Raman spectra of the liquid and is in line with ΔE values for longer n‐alkanes in the liquid state. However, there is a large difference between the value reported here for liquid n‐butane and that reported for the gas (∼966 cal/mole).

Water in polymer membranes. Part I : Water sorption and refractive index of cellulose acetate

Abstract The dependence of water absorption of 2 to 4 μm thick membranes of cellulose acetate on relative humidity was determined by measuring small changes in their asymmetric waveguide properties in the visible spectral region. Simultaneous measurements of changes in film thickness provide a direct method for obtaining the change in film volume as a function of water concentration and a new measure of polymer porosity. Data are presented for a typical film fabricated from cellulose acetate (CA398-30) which illustrate the usefulness of studying water absorption by integrated optics techniques.

Water in polymer membranes. Part II : Raman scattering from guided laser beams

Abstract Simultaneous application of integrated optics and Raman spectroscopy is used to investigate the hydrogen bonding of water in thin dense symmetric membranes of cellulose acetate (CA). A modified X-ray quarter circle goniometer is used to measure refractive index, film thickness, and Raman spectra using guided laser beams and the prism coupler technique. The film remains in a fixed position during all measurements thereby ensuring identical light collection geometries for Raman scattering observed from different wave-guiding modes. To illustrate the technique, Raman scattering of a 3.5 μm film of CA398-10 in the OH stretching region is shown as a function of relative humidity (RH). These spectra show that water sorbed at less than 50% RH is weakly hydrogen-bonded but above 50% RH, sorbed water has the strongly hydrogen-bonded properties of bulk water.

Intermolecular coupling in liquid water

Changes in the Raman spectra of H2O from addition of OD oscillators indicate that there is significant intermolecular coupling of OH stretching vibrations in H2O at temperatures from −10 to 70°C. Measurements on solutions of KI in H2O indicate that the primary effect of salt addition on the spectrum of H2O is to diminish intermolecular coupling of OH oscillators. The disruption of intermolecular coupling by addition of a K+ and I− ion is about nine times more effective than addition of a single OD oscillator.

A Computer Controlled Raman Spectrometer System

We describe a software system and a hardware interface between a laser Raman spectrometer and a time-shared computer. This data acquisition system controls the wavelength drive of the spectrometer and the analyzer orientation using stepping motors and position sensors. With this method accurate depolarization ratios can be determined at every wavelength increment. Digitized photon counting gives good signal/noise ratios and a wide dynamic range for Raman intensity measurements. The software design permits automatic separation of isotropic and anisotropic spectra, repetitive counting periods, instant scope display of raw, reduced or integrated data, and numerous data refinement options.

On the determination from Raman spectra of the polarizability derivative with respect to the O–D bond stretching coordinate in the ices

Several different measurements 1,2,3,4 of the integral intensities in the Raman spectra of polycrystalline ice are discussed. The polarization derivatives derived from the intensity measurements are compared. (AIP)