The Intensities of Methane in the 3-5 µm Region Revisited

The analysis of the linestrengths of the infrared spectrum of methane (12 and 13) in the 3-5 μm region has been revisited on the basis of new measurements from Fourier transform spectra recorded at Kitt Peak under various optical densities. A simultaneous fit of these new data with previously reported tunable difference-frequency laser data has been done. An effective transition moment model in tensorial form up to the third order of approximation within the Pentad scheme has been used. The standard deviations achieved are very close to the experimental precision: 3 and 1.5%, respectively, for the two sets of data for the (12)CH(4) molecule, representing a substantial improvement with respect to earlier studies. The integrated bandstrengths obtained in the present work differ from previously reported values by factors ranging from -5 to +6%. The correction for the nu(3) band, the strongest band of the Pentad system, is +2% with respect to the study of Hilico et al. [J. C. Hilico, J. P. Champion, S. Toumi, V. G. Tyuterev, and S. A. Tashkun, J. Mol. Spectrosc. 168, 455-476 (1994)]. Copyright 2000 Academic Press.     

Investigation of local order in unreacted DGEBA epoxy resin monomers by light scattering

The existence of local order in two epoxy resins of the diglycidyl ether of bisphenol-A (DGEBA) type has been investigated using Rayleigh scattering and Brillouin spectroscopy. The resins differ in their molecular weight distributions and their relative concentrations of epoxide and hydroxyl groups. The complementary use of both techniques in elucidating the thermal behavior of local order is illustrated, and the use of the latter technique to study thermal acoustic phonons and hypersonic relaxation is discussed. Both techniques independently show that molecular aggregates exist in each resin system. The scattering-envelope dissymmetry shows that the resin with the high epoxide/hydroxyl group ratio contains aggregates up to 20 nm in size, and the low-ratio resin exhibits sizes up to 70 nm. These aggregates are thermally unstable in the temperature range studied (293–443 K). Dissolution in chloroform shows that these aggregates are reduced in size and that further structural changes occur which are dependent on solvent concentration. Aggregate volume fractions were determined for a range of aggregate size. Brillouin spectroscopy indicated that both resins exhibit hypersonic relaxation in the temperature range studied. The complex longitudinal moduli of the resins were superimposable under a WLF temperature transformation comparable to the difference in their static glass transition temperatures. Molecular aggregate size, number, and stability are related to the epoxide/hydroxyl ratio of the resins and the degree of intermolecular hydrogen bonding.     

Analysis of the ν3 and ν1 infrared bands of GeH4

The high-resolution infrared spectrum of GeH₄ in the region 2020 to 2200 cm^?1 was analyzed. Most of the observed lines were assigned to transitions of the ν₃ and ν₁ bands of the five naturally occurring isotopic species. The spectrum was fitted by diagonalizing the v₃ = 1 and v₁ = 1 Hamiltonians coupled by the dominant vibration-rotation interaction term. For each isotopic species, about 100 transitions were fitted with an overall standard deviation of 0.006 cm^?1, using only 10 adjustable parameters. The five sets of parameters obtained are consistent with the expected isotope effects.     

Vibration-rotation energies of harmonic and combination levels in tetrahedral XY4 molecules: Analysis of the 2ν2 and ν2 + ν4 bands of 12CH4

The theory and the extrapolation method described in the previous paper are used to analyze the v₂ = 2 and v₂ = v₄ = 1 levels of ¹²CH₄. In addition to the well-known parameters of the ground, v₂ = 1, and v₄ = 1 states, the computation of energy levels involves only 6 new parameters for 2ν₂ and 13 for ν₂ + ν₄ up to the fourth order of approximation. These parameters have been determined from Raman and infrared data. Forty-four Raman lines observed by Berger in the region from 3060 to 3090 cm^?1 have been assigned to the 2ν₂ band. The standard deviation obtained by fitting 39 of these transitions with the 6 corresponding parameters is 0.025 cm^?1. The calculated frequencies of ν₂ + ν₄ are compared with moderate resolution ir spectra recorded in our laboratory and the recent spectra of Hunt et al. Totally polarized weak Raman lines observed by Berger in the region from 2850 to 2900 cm^?1 have been assigned to the ν₂ + ν₄ band arising through a second-order Coriolis interaction with the ν₁ band. A project of a comprehensive treatment of the energy levels of methane between 2550 and 3650 cm^?1 is discussed.     

Strengths of single lines in the 12C16O2, ν3 band at 4.3 μm

Individual line strengths have been measured in the 4.3-μm ν₃ absorption band of ¹²C¹⁶O₂ from R46 to R90 using a vacuum grating spectrometer. Approximately 1100 measurements were made at pressures from 0.16 to 100.0 Torr, path lengths from 3.25 to 2331 cm, and temperatures from 246 to 338 K. The standard deviations of the measurements varied from 5 to 10%. The mean value of the vibrational dipole matrix element squared obtained is {R_if}² = 0.1103 ± 0.0085 D².     

High-performance liquid chromatographic separation of the enantiomers of organophosphorus pesticides on polysaccharide chiral stationary phases.

High-performance liquid chromatographic separation of the individual enantiomers of 12 organophosphorus pesticides (OPs) was obtained on polysaccharide enantioselective HPLC columns using alkane-alcohol mobile phase. The OP pesticides were crotoxyphos, dialifor, fonofos, fenamiphos, fensulfothion, isofenphos, malathion, methamidophos, profenofos, crufomate, prothiophos and trichloronate. The enantiomers of fenamiphos, fensulfothion, profenofos and crufomate were separated on CHIRALPAK AD; the enantiomers of fenamiphos were also separated on CHIRALPAK AS; the enantiomers of methamidophos, crufomate and trichloronate were separated on CHIRALCEL OD; the enantiomers of crotoxyphos, dialifor, fonofos, malathion, prothiophos and trichloronate were separated on CHIRALCEL OJ; and the enantiomers of isofenphos were separated on CHIRALCEL OG. Baseline or partial separation of the enantiomers of six of these OP pesticides was obtained on CHIRALCEL OJ. In continued method development, the separation of the enantiomers of the 12 OPs was investigated more extensively on CHIRALCEL OJ to determine whether the mobile phase composition, flow-rate and column temperature could be optimized to yield at least partial separation of the enantiomers. Chromatographic conditions were found that gave either baseline or near baseline separations of the enantiomers of the 12 OPs on the CHIRALCEL OJ column.     

Consistency of the free-volume approach to the homogeneous deformation of metallic glasses

One of the most widely used approaches to model metallic-glasses high-temperature homogeneous deformation is the free-volume theory, developed by Cohen and Turnbull and extended by Spaepen. A simple elastoviscoplastic formulation has been proposed that allows one to determine various parameters of such a model. This approach is applied here to the results obtained by de Hey et al. on a Pd-based metallic glass. In their study, de Hey et al. were able to determine some of the parameters used in the elastoviscoplastic formulation through DSC modeling coupled with mechanical tests, and the consistency of the two viewpoints was assessed.