V3 Band Research Articles

Middle and upper atmosphere pressure‐temperature profiles and the abundances of CO2 and CO in the upper atmosphere from ATMOS/Spacelab 3 observations

Based on a new approach, profiles of kinetic temperature and atmospheric pressure between 20 and 116 km altitude and CO2 and CO volume mixing ratios between 70 and 116 km have been derived from the ∼0.01‐cm−1 resolution infrared solar occultation spectra recorded by the atmospheric trace molecular spectroscopy (ATMOS) Fourier transform spectrometer during the Spacelab 3 shuttle mission (April 29 to May 6, 1985). The physical model and CO2 profile results have been obtained from simultaneous multiscan least squares fitting of microwindows containing CO2 lines with temperature‐dependent and temperature‐independent intensities and N2 lines with temperature‐independent intensities. The analysis included the retrieval of tangent height separations between spectra in the lower stratosphere, where independent information shows drifts of the sun tracker field of view on the solar disk. The physical model results are compared with climatological profiles, lower thermospheric temperatures computed with the MSISE‐90 model, and other data. The CO2 retrievals indicate a nearly constant volume mixing ratio of 320 ± 35 ppmv (parts per million, 10−6, by volume) in the 70‐to 90‐km altitude region with a rapid decline in the CO2 volume mixing ratio beginning between 90 and 100 km; at 116 km the CO2 volume mixing ratio has declined to about 70 ppmv and is equal to the CO volume mixing ratio, which has been derived from fits to the (1‐0) CO vibration‐rotation band. The absorption by the v2 + v3 ‐ v2 band of CO2 has been analyzed to quantify nonlocal thermodynamic equilibrium (non‐LTE) effects in the upper mesosphere and lower thermosphere. Up to an altitude of 100 km, the results indicate that the vibrational temperature of the v2 state of CO2 is within 5 K of the kinetic temperature. At higher altitudes, non‐LTE effects are observable with the vibrational temperature of the v2 state cooler than the kinetic temperature by 40 K (48°S) and 70 K (30°N) at 112 km. Above 112 km, lines of the v2 + v3 ‐ v2 band are too weak to be observed in the ATMOS spectra.

Raman spectroscopy of PH3 and PH2 at high temperature and simulation of PH3 Raman spectrum

AbstractExperimental Raman spectra of the symmetric stretching vibration band v1 and of the degenerate stretching vibration band v3 of PH3 were obtained for temperatures ranging from 293 to 903 K. These spectra also show a band of a new gaseous species, which is a pyrolysis product of PH3. This band can be unambiguously attributed to PH2. To extract the Raman spectrum of PH2 from the overall spectrum, the PH3 Raman spectra of the v1 and v3 bands were calculated. The way in which these bands were calculated is explained and a comparison is made between the experimental and simulated spectra at different temperatures. These comparisons clearly identify the PH2 v1 band. By the subtraction of the simulated spectrum from the experimental spectrum, the origin of the PH2 v1 band is estimated to be 2310.3 ± 2 cm−1.

Coherent Anti-Stokes Raman Spectroscopy of the Stretching Vibrations of the Water Isotopomers

Coherent anti-Stokes Raman spectroscopy (CARS) has been employed to study the v1 band of H2O, v1 band of DzO, and v1 and v3 bands of HOD in the gas phase at room temperature and at moderate resolution. These molecules are characterized by a complicated spectrum which is not completely rotationally resolved. A method for the deconvolution of incompletely resolved CARS spectra has been utilized, in which a Boltzmann population distribution is assumed. The calculated spectrum nearly exactly reproduces the observed spectrum and allows assignment of the rotational transitions which are observed in the spectra. All the transitions that appear in these spectra belong to the isotropic Q branches. The CARS spectra of D2O and HOD are studied here for the first time.

Infrared diode laser absorption features of N2O and CO2 in a laval nozzle

Design and operation of a pulsed Laval nozzle and the characterization of molecular flow through such a nozzle using IR tunable diode laser (TDL) is the central theme of this work. The results here deal with He diluted N2O and CO2 gaseous systems. Boltzmann type plots of the spectral intensity data of both N2O and CO2 show non-linear behaviour. We have attempted to understand this non-linear behaviour of Boltzmann plots in terms of (1) instability in the jet and (2) a two-temperature model for the flowing gas, a cold central core and a hot boundary layer close to the nozzle walls. The model based on jet instability represents the data somewhat poorer than the two-temperature model. The parameters derived from fitting our experimental data to the former model could be used to calculate the thermodynamic parameters only through further approximations. Measured absorption line profile of the P(15) line of the v2 band of N2O as a function of axial distance from the nozzle exit gradually shifts from a Lorentzian to a Gaussian type. Velocity distribution of N2O molecules in a Laval nozzle is determined by differentiating the absorption line profile of the P(15) line (v0=576.235 cm−1) of the v2 band of N2O. Translational temperature of N2O molecules is determined from the observed spectral profiles.

Anomalous Pressure Dependence of Infrared Spectra Due to the Combination of Collisional Broadening and Instrument Resolution

The combination of collisional line broadening and limited instrumental resolution can have peculiar and unexpected effects on the intensities of infrared spectra. An illustrative example is provided by the series of Q branches in the v7 band of ethane. Conventional FT-IR spectra, with a resolution of ∼0.25 cm−1, show a dramatic increase in the absorbance of these branches as a function of increasing N2 partial pressure, an effect which could be construed as collisional narrowing. In contrast, high-resolution diode laser spectroscopy reveals a monotonie increase in branch width (0.14 cm−1/atm), and a concomitant decrease in intensity, as the N2 pressure is raised. The present work shows that absorption measurement of the inherently very narrow ethane Q branches with limited instrumental resolution and collisional line broadening conspire to give the appearance that the absorbance increases with N2 pressure. This effect in general, as well as its implications for the use of FT-IR spectroscopy to measure molecular concentrations in gaseous mixtures, is discussed.

High‐resolution photoacoustic Raman spectroscopy of gases

AbstractA high‐resolution photoacoustic Raman spectroscopy experiment is described. The resolution achieved by using two single‐mode pulsed lasers is about 0.0054 cm−1 (full width at half maximum intensity). The experiment was tested first on the v1/2v2 bands of CO2 and gave an increase of at least about one order of magnitude in the signal‐to‐noise ratio with respect to stimulated Raman spectroscopy at low pressure (ca. 10 Torr ≈ 1.3 kPa). The sensitivity is also demonstrated by the study of the weak hot band v1 + v2 — v2 of CO2. In both cases, the experimental line shape is well reproduced by taking into account Doppler and collisional effects. A comparison with CARS spectra was also made.

Stratospheric HNO3 measurements from 0.002‐cm−1 resolution solar occultation spectra and improved spectroscopic line parameters in the 5.8‐μm region

Measurements of stratospheric HNO3 are presented based on new very high resolution (0.002‐cm−1 full width at half maximum (FWHM)) solar occultation spectra recorded at 32°N latitude with a balloon‐borne interferometer in the region of the HNO3 v2 band at 5.8 μm and improved spectroscopic line parameters generated for this HNO3 band and the interfering bands of O3 and H2O. The line parameters for HNO3, computed from the spectroscopic constants reported by Maki, are a significant improvement in that the calculated positions are more accurate than previous data and the line list now includes higher J and Ka transitions needed to account for weaker HNO3 absorption features observable in the stratospheric spectra. Verifications of the new line parameters based on the stratospheric spectra and a 0.002‐cm−1 resolution HNO3 laboratory spectrum are presented along with comparisons generated with the parameters from the 1986 HITRAN compilation. Significant improvements are apparent for all the updated bands. Finally, the stratospheric HNO3 profile retrieved from the stratospheric solar spectra using a nonlinear least squares fitting algorithm and the new line parameters is reported and compared with previously reported measurements.

Infrared spectroscopic investigations of the calcite-rhodochrosite and parts of the calcite-magnesite mineral series

The infrared spectroscopic measurements of synthetic and natural carbonate samples show that significant frequency shifts in the v2 and v4 vibrational bands of the carbonate ion group occur in the calcite-rhodochrosite and calcite-magnesite mineral series as a function of the chemical composition. These shifts are due to cationic substitution, reflecting the different ionic raddii and masses of the end-members. A tentative model for the variations of v2 and v4 in the ternary system CaCO3−MnCO3−MgCO3 is presented.

V centers produced in KI crystals under KrCl excimer laser irradiation

Abstract Irradiation of KI near 150 K with KrCl excimer laser irradiation (hv=5. 58 eV) produces V centers causing V2 and V3 bands. The two bands exhibit 100-type dichroism. In KI containing V centers, the 111 cm−1 Raman signal attributed to I3- molecular ions is observed. Under KrCl excimer laser irradiation at low temperatures, resonance Raman scattering effects have been also studied for KI, NaI and LiI.

Novel infrared spectroscopic method for the determination of crystallinity of hydroxyapatite minerals

Biologically important apatite analogues have been examined by Fourier Transform Infrared Spectroscopy (FT-IR), and a method developed to quantitatively assess their crystalinity. Changes in the phosphate v1 and v3 regions, 900-1,200 cm-1, for a series of synthetic (containing hydroxide, fluoride, or carbonate ion) and biological apatites with crystal sizes of 100-200 A were analyzed with curve-fitting and second derivative spectroscopy. The v1,v3 contour was composed of three main subbands. Correlations were noted between two spectral parameters and crystal size as determined by x-ray diffraction. The percentage area of a component near 1,060 cm-1 decreased as the length of the c-axis of the hydroxyapatite (HA) compounds increased, while the frequency of a band near 1,020 cm-1 increased with increasing length of the apatite c-axis. These parameters are thus proposed as indices of crystallinity for biological (poorly crystalline) HA. The FT-IR spectra of highly crystalline apatitic compounds were also analyzed. For crystal sizes of 200-450 A, the percentage area of the phosphate v1 band (near 960 cm-1) decreased with increasing HA crystal size. IR indices of crystallinity have thus been developed for both well crystallized and poorly crystallized HA derivatives. The molecular origins of the various contributions to the v1,v3 contour are discussed, and a preliminary application of the method to a microscopic biological sample (rat epiphyseal growth plate) is illustrated.

Diode-laser measurements of collisional line broadening in the v5 band of C 2H 2

Self-broadening coefficients for 27 lines of acetylene in the P- and R-branches of the v 5 band have been measured at room temperature with a tunable diode-laser spectrometer. We have first calculated these broadening coefficients on the basis of two semi-classical impact models by using a simple intermolecular potential. The quadrupole moment of C 2H 2 as well as a dispersion parameter have then been determined by fitting the calculated results of our experimental data. We next use the approach of Robert and Bonamy in which the intermolecular potential does not include adjustable parameters and involves the addition of an atom-atom interaction model to the electrostatic interactions. The usual spherical harmonics expansion of the atom-atom potential appears to be quite inadequate at short distances. The results of calculations derived from a rough consideration of the exact radial expansion of the atom-atom potential lead to better agreement for high J lines than those derived from the truncated expansion. It is also shown that the electrostatic contributions arising from the hexadecapole moment of C 2H 2 are only significant for | m| > 20.

Identification of 4- to 7-quantum v3 bands in the atmospheric recombination spectrum of ozone

Spectra of ozone hot band chemiluminescence obtained in the SPIRIT 1 rocket experiment have been analyzed with the aid of laboratory data and vibrational energy and band contour predictions. Band centers and energies for previously unreported vibrational states of ozone having up to seven quanta have been derived. The assignments are supported by the predictions of an improved Darling-Dennison-type energy level formula which behaves realistically towards dissociation. Bands associated with bending as well as stretching excitation appear due to an accidental vibrational resonance and a non-mode-specific population distribution.

Spectroscopic line parameters for the ν_6 band of carbonyl fluoride

New measurements and analysis of high resolution(0.0025 cm(-1)) laboratory spectra of the carbonyl fluoride v6 band are described. The data are used to generate line parameters suitable for high resolution atmospheric studies.

Peculiarities of the Ionic Dynamics of Molten Nitrites

Abstract Polarization measurements in the Raman spectra of molten sodium nitrite have shown that the reorientational line widths of the v1 and v2 bands (both of the A1 symmetry type) of NO2̄ are different. Possible reasons are discussed. Also, the line widths of NO2̄ for various molten nitrites are found to depend on R-4 , the cloasest approach distance in the melt, and on Z, the cation charge number. This dependence agrees with theoretical predictions for the coupling of vibrational and reorientational dephasing caused by ion-dipole interactions.

Diode laser measurements of He-broadened linewidths in the v1 band of OCS

He broadened halfwidths of 26 lines in the v 1 band of OC 32S have been measured from absorption spectra recorded at room temperature with a tunable diode-laser spectrometer. The results are compared with values calculated on the basis of the Anderson- Tsao-Curnutte theory and an improved semi-classical impact model developed by Robert and Bonamy. Both models have been applied by using a Smith-Giraud-Cooper intermolecular potential. Different sets of values for the potential parameters have been determined by fitting the calculated results to experimental data.

Secular increase of the vertical column abundance of methane derived from IR solar spectra recorded at the Jungfraujoch station

Using all of the pertinent infrared solar spectra recorded at the Jungfraujoch Station, Switzerland, in 1951, 1975, and in 1984–1987, the increase of the vertical column abundance of methane, CH4, above that station has been reevaluated. The results are based on equivalent widths measurements of both the R0 and the R5 transitions of the 2v3 band of CH4 at 6015.66 and 6067.09 cm−1 and on the CH4–v3 band absorption characteristics between 2905.0 and 2908.8 cm−1. The data between 1984 and 1987 provide a full seasonal cycle. They demonstrate a significant annual variation in the column abundance of CH4 of ±10% around the mean. They also show variability on shorter time scales. The mean cumulative rate of increase of the total vertical column abundance of CH4 above the Jungfraujoch is found to be (0.7 ± 0.1)% yr−1 between 1951 and 1986. Using a realistic CH4 concentration profile throughout the troposphere and the stratosphere, we deduce volume mixing ratios at the altitude of the Jungfraujoch, equal to 1.28±0.08 and 1.64±0.09 ppm, for 1951 and for 1985–1987, respectively.

Thermal and other studies on bivalent metal selenltes

BaSeO3·2·5H2O(I), PbSeO3· 2H2O(II) and CdSeO3·3.5H2O(III) were prepared and analysed. Their hygroscopicity and solubility was investigated. These compounds have high thermal Stability, as shown by their TG and DTA data. IR spectra show multi-dentate coordination of selenite to cations, due to considerable splitting of the asymmetric v3 and v4 bands of SeO 23 − in the 780-730 cm−1 and 420-325 cm−1 region.Tentative structures have been proposed involving bridging oxygen atoms.

Tunable diode laser measurements of absolute line strengths in the 2 v2 band of N 2O near 8μm

The absolute intensities of five rotational transitions in the 2 v 2 band of N 2O near 8 μm have been measured with a tunable-diode laser-spectrometer. Measurements were reproducible within an average deviation of about 3%, and the experimental and calculated line strengths differed by only 1.5%. An analysis of the line strengths has yielded a band strength of S v = 6.98 ± 0.26 cm -2 atm -1 at 296 K. Our band and line strengths are in excellent agreement with two recently reported values obtained by using Fourier transform-i.r. spectroscopy.

Study of the spectrum of CH3 35C1 between 4250 and 4600 CM?1: thev 2+v 4 andv 4+v 5 rovibrational bands

About 2500 lines of CH335Cl have been assigned. The strong xy Coriolis resonance between thev2 andv5 modes is quite visible between thev4+v4±1 perpendicular band, centered around 4383 cm−1, and thev4±1+v5±1 perpendicular component, centered around 4475 cm−1, with a crossing of upper energy levels allowing the observation of lines which are normally forbidden. Although not yet observed with certainty, because of the great density of lines of the spectrum, thev4∓1+v5±1 parallel component is nevertheless detectable by its effects onv2+v4±1 which is linked by Coriolis resonance to both components ofv4+v5. Moreover the spectrum is much complicated by many other resonances with weak bands which occur at level crossings: it is the case ofv2+3v6±1, connected tov2+v4±1 by the well known Darling Dennison resonance which couplesv4±1 and 3v6±1, and also ofv5±1+3v6±1 connected tov4±1+v5±1 by the same resonance; but this last case is complicated by an anharmonic resonance betweenv5±1+3v6±1 and 2v3+3v6∓1. Two more perturbations occur on the ΔK=−1 side ofv2+v4: a weak Coriolis resonance gives rise to one subband ofv1+v2 at a level crossing withv2+v4, and thev1+v5 band (linked of course tov1+v2 by the Coriolis resonance between thev2 andv5 modes) is quite visible and perturbs several subbands ofv2+v4 of high values of K through an anharmonic resonance. Moreover, the complex (3v5±1,v+2v50, 2v2+v5±1, 3v2,v2+2v5±2, 3v5±3) system of Coriolis-connected bands is linked to the bands studied in the present work by two Fermi resonances: one betweenv2+2v50 andv1+v2, and the other one betweenv1+v5 and 3v5±1, whose several subbands have been observed on the low part of the spectrum. The values of all the band centres and of the different coupling constants have been estimated, but all these interactions make the line assignments and the interpretation of the spectrum very difficult.

Infrared Studies of Long-Range Stress in Solid-State Peroxide Photoreactions

Abstract When crystals of di(undecanoyl) peroxide are photolyzed at low temperature to conversions greater than about 0.06%, in situ FTIR spectroscopy of the CO2 product shows numerous v3 bands which are not observed after less extensive photolysis. The shift of these bands to high frequency suggests the influence of stress fields generated by distant reaction sites. The influence becomes more pronounced upon annealing to about 140K, but disappears after annealing above 280K. This behavior is discussed in terms of relaxation through both rapid elastic deformation and stepwise, thermally activated plastic deformation. Isotope labeling shows that the new CO2 vibrations are not tightly coupled to one another. An analysis based on random decomposition shows that the perturbing defects lie well beyond the first coordination sphere of the probe CO2 molecule and probably cooperate in influencing subsequent reactions. These results suggest caution in interpreting solid state product distributions, even at very lo...