V3 Band Research Articles

High resolution FTIR spectroscopy of CFC's in a supersonic jet expansion

High resolution FTIR spectra of dichlorodifluoromethane and bromochlorodifluoromethane have been recorded on a Bruker HR120 spectrometer coupled to a supersonic jet nozzle apparatus. Rotational temperatures of 40K for Freon-12 and Halon-1211 have been achieved. An analysis of the v1 band of Freon-12 has been carried out.

Self-broadening coefficients and line strengths in the v3 band of CH 335C1 at low temperature

Self-broadened linewidths have been measured in the P- and R-branches of the v 3 band of CH 3 35Cl at 200 K using a tunable diode-laser spectrometer. The lines under study are located in the spectral range 706–751 cm -1, with J values ranging from 3 to 27 and K from 3 to 6. The collisional half-widths were estimated along with the corresponding line strengths by fitting measured shapes of the individual lines with Voigt profiles convolved with the instrumental function. The line strengths at 200 K are in satisfactory agreement with results derived from previous measurements. Even though semi-classical calculations of line-broadening involving electrostatic interactions have yielded half-widths at 200 and 296 K that are greater than experimental data for low or medium values of J, they seem to predict correctly the K-dependence of the broadening coefficients of lines with the same J transition as well as their temperature dependence.

The C=O Stretching Frequency in the S1 (π* ‐ n) State of Acetaldehyde and its Deuterated Derivatives Determined With the Photofragment Excitation Spectroscopy

The vibrational structure was recorded for the S1 (π* ‐ n) state of acetaldehyde (CH3CHO) and its deuterated derivatives (CH3CDO, CD3CHO and CD3CDO up to ∼3500 cm-1above the 0‐0 bands with the LIF (laser induced fluorescence) and PHOFEX (photofragment excitation) techniques. In the PHOFEX spectroscopy, the yield of the formyl radical, HCO() or DCO(), produced in the photodissociation of acetaldehyde is measured against the excitation frequency. The yield was determined by monitoring one of the rotational lines in the ← transition of the formyl radical by the LIF technique. This is the first measurement of the vibronic structure of acetaldehydes in supersonic jets above the dissociation threshold where they are non‐fluorescent. The results have made it possible to locate v4 (the C=O stretching) and 2v4 bands unequivocally; the v4 fundamentals at 1217, 1189, 1210 and 1178 cm-1 above the 0‐0 band for CH3CHO, CH3CDO, CD3CHO and CD3CDO, respectively. The corresponding overtone (2v4) bands are observed, respectively, at 2414, 2350, 2399 and 2334cm-1. All the vibronic bands newly observed in the PHOFEX spectra are found to be interpreted as the combinations of v4 and 2v4 with the modes appearing in the lower frequency (< 1200 cm-1) region, which consist of v10 (the C—C—O in‐plane bending), v14 (the C=O out‐of‐plane wagging) and v15 (the methyl torsion).

Noble gas pressure broadening in the v1 and v3 band of SO 2 studied with IR tunable diode laser spectroscopy

Detailed investigations of the pressure broadening of SO 2 for collisions with the noble gases He, Ne, Ar and Kr are presented. The broadening coefficients of 14 lines in the v 1 band near 1151 cm −1 (13 ⩽ J″ ⩽ 44, 3 ⩽ K″ a ⩽ 19) and 8 lines in the v 3 band near 1361 cm −1 (4 ⩽ J″ ⩽ 61, 0 ⩽ K″ a ⩽ 17) were determined using a tunable diode laser spectrometer. In the v 1 band the broadening coefficients γ( J″, K″ a ) for the individual lines range from 0.056 to 0.086 cm −1 atm −1 for collisions with He, from 0.045 to 0.069 cm −1 atm −1 for Ne, from 0.062 to 0.092 cm −1 atm −1 for Ar, and from 0.078 to 0.12 cm −1 atm −1 for Kr. In the v 3 band they lie between 0.035 and 0.13 cm −1 atm −1 for He as the perturber, between 0.041 and 0.086 cm −1 atm −1 for Ne, between 0.05 and 0.11 cm −1 atm −1 for Ar, and between 0.076 and 0.11 cm −1 atm −1 for Kr. The broadening coefficients have an accuracy between 1.5 and 10%. We compare the determined values with former results obtained in the v 3 band of NO 2. The tendency for most of the SO 2 lines demonstrates that the Kr-broadening coefficient is larger than the Ar-broadening coefficient in contrast to NO 2.

Infrared diode laser probing of methane in excimer laser photolysis of pyruvic acid

The photodissociation of pyruvic acid at 193 nm has been studied and one of the photoproducts, methane, was detected using an infrared diode laser absorption probe technique. Using second-derivative absorption spectroscopy at 1346.326 cm-1[R (-)(7) transition in v4 band], the progress of the reaction was monitored. The quantum yield of formation of methane = 0.09 ± 0.01 and was further corroborated by a simple measurement of pressure changes following the photolysis. The secondary photolysis of the photoproduct acetaldehyde via the established route was found to be negligible. This result may help to account for the energetics of the photodissociation process by a 6.4 eV excimer laser photon. The possibility of using this technique to examine the nascent methane molecule in real-time domain to gain better insight of the dissociation dynamics is also indicated.

Mössbauer and Infrared Studies of the Ferrite System Co0.6Zn0.4CuxFe2−xO4

The ferrite system Co0.6Zn0.4CuxFe2−xO4, 0 ≤ x ≤ 1, is studied by Mössbauer spectroscopy at room temperature, infrared spectra, and mobility measurements. The Mössbauer studies show that the samples are ferrimagnetic for all values of x; the hyperfine parameters of the tetrahedral and octahedral sites are determined as functions of x and so the cation distributions and spontaneous magnetization are deduced. Four bands are observed in the IR spectra. The high-frequency band v1 is assigned to the tetrahedral cations and the low-frequency band v2 to the octahedral complexes. The small band v3 is assigned to the divalent octahedral metal ion. The lowest band v4 is attributed to the lattice vibrations of the system. The drift mobility at different temperatures is determined for all compositions of our system and the activation energies are deduced.

The 3 v3 band of CO 2—influence of the pressurized perturber gas

The modification of the shape of the 3 v 3 vibration-rotation band of CO 2 by different perturbing gases (CO 2, He, Ar, N 2) has been studied at room temperature for a wide range of pressures (up to 140 atm) using a Fourier transform interferometer. Important narrowing effects in the R branch are observed.

Identification of Three Absorption Bands in the 2-μm Spectrum of Io

Spectroscopic observations of the trailing face of Io at a resolution of 1.02 cm-1 performed with the FTS on the 3.6-m Canada-France-Hawaii telescope on Mauna Kea confirm the presence of two weak absorption features in the 2-μm region. The first feature occurs at 4704.9 ± 0.2 cm-1 (2.12545 ± 0.00010 μm); it is about 6.8% deep and 3 cm -twide (FWHM). The second feature is at 5047.1 ±1 cm-1 (1.98135 ± 0.0004 μm) with a broad central core; its depth is about 8% and its width approximately 7 cm-1. A laboratory investigation of spectra of solid SO2 with relatively thick samples, as well as of mixtures of SO2 with CO2 and H2S, indicates that the two features at 4705 cm-1 and 5047 cm-1 are best explained by the 3v1 + v3 and v1 + 3v3 modes of solid SO2 around 130 K, respectively. Previous work tentatively proposing CO2 clusters as an explanation for the first feature and condensed H2S for the second can no longer be supported. In addition, a careful a posteriori look at our Io spectrum shows the presence of a band at 3933 ± 1 cm-1 (2.5426 ± 0.0007 μm) (depth ≈ 30%, FWHM ≈ 8 cm-1) due to the 3 v3 band of solid SO2, as predicted by our laboratory experiments. The positions and widths of these bands indicate that a temperature gradient may exist between the surface of the frost and several centimeters below and suggest that some SO2 may be mixed at the molecular level with some neutral component. Three different models are proposed to explain the apparent discrepancy between the large variability with 1ongitude of the strong 2457 cm-1 (4.07 μm) band and the nearly constant depth of the weak 4705 cm-1 (2.1254 μm) band. All three models lead to mean grain sizes from a few hundreds of micrometers to about 1 mm. The first model invokes a large variation in grain sizes (factor 2-3) over lo's hemispheres. This model correctly fits the observed depths of the 2. and 4.07-μm bands but not that of the 3.78-μm (2645 cm-1) band. The second model assumes a considerable variation in thermal flux with Io's longitude (at 2457 cm-1, up to 20% of the reflected continuum flux). This model can reconcile the band strengths in the whole 2- to 4-μm range with about the same grain size at all longitudes and with moderate variations in frost coverage, but does not explain the albedo variability in the UV range. The third model assumes an uniform layer of coarse grained SO2 frost (a few hundred micrometers in size) with a variable longitudinal coverage of a thin layer of very fine frost grains (less than a few millimeters of micrometer-sized grains). This model qualitatively explains the observed IR and UV variations. Using the optical constants of solid SO2 measured in the laboratory, we predict the position and depth (≥-1%) of about 25 additional absorption features of SO2 frost, in the 2800-5000 cm-1 (2.0-3.6 μm) range, that should be observed in future high quality spectra of Io.

Determination of broadening coefficients and intensities for overlapping spectral lines with application to the QR (3, K) lines in the v3 band of CH 353Cl

We have developed a method of extracting individual line parameters from overlapping absorption spectra recorded with a tunable diode-laser spectrometer. Assuming Voigt profiles for the individual lines, the overall absorption is expressed as the sum of the absorption coefficients of the recorded lines plus a small contribution due to neighboring lines. The computational procedure has been applied to the four QR (3, K) lines, self-broadened and broadened by N 2,O 2, Ar and He, in the v 3 band of CH 35 3Cl at 736.3 cm -1. The intensities and collision-broadened widths are found to be linear functions of the broadener pressures, which implies negligible line-mixing effects between the K components. For all the perturbers considered the broadening coefficients of the QR (3, K lines decrease significantly as K increases, in agreement with theoretical results.

Diode Laser Measurements of Self-Broadening Coefficients in the v5-Band of C2H2 at Low Temperature

Collisional self-broadening coefficients for 21 lines in the P and R branches of the v5 band of C2H2 at low temperature (173 K) have been measured using a tunable diode laser spectrometer and a low-temperature variable path length absorption cell. These lines, with J values ranging from 1 to 25, are located in the spectral range 670-790 cm−1. A semiclassical line-broadening calculation provides satisfactory results when the electrostatic interactions arising from the hexadecapole moment of C2H2 are taken into account. We have also examined the validity of a simple power law governing the temperature dependence of the broadening coefficients.

Fourier transform Raman spectroscopy of synthetic and biological calcium phosphates.

Fourier-transform (FT) Raman spectroscopy was used to characterize the organic and mineral components of biological and synthetic calcium phosphate minerals. Raman spectroscopy provides information on biological minerals that is complimentary to more widely used infrared methodologies as some infrared-inactive vibrational modes are Raman-active. The application of FT-Raman technology has, for the first time, enabled the problems of high sample fluorescence and low signal-to-noise that are inherent in calcified tissues to be overcome. Raman spectra of calcium phosphates are dominated by a very strong band near 960 cm-1 that arises from the symmetric stretching mode (v1) of the phosphate group. Other Raman-active phosphate vibrational bands are seen at approximately 1075 (v3), 590 (v4), and 435 cm-1 (v2). Minerals containing acidic phosphate groups show additional vibrational modes. The different calcium phosphate mineral phases can be distinguished from one another by the relative positions and shapes of these bands in the Raman spectra. FT-Raman spectra of nascent, nonmineralized matrix vesicles (MV) show a distinct absence of the phosphate v1 band even though these structures are rich in calcium and phosphate. Similar results were seen with milk casein and synthetic Ca-phosphatidyl-serine-PO4 complexes. Hence, the phosphate and/or acidic phosphate ions in these noncrystalline biological calcium phosphates is in a molecular environment that differs from that in synthetic amorphous calcium phosphate. In MV, the first distinct mineral phase to form contained acidic phosphate bands similar to those seen in octacalcium phosphate. The mineral phase present in fully mineralized MV was much more apatitic, resembling that found in bones and teeth.(ABSTRACT TRUNCATED AT 250 WORDS)

Diode-laser measurements of self-broadening coefficients and line strengths in the v3 Band of CH 335Cl

Self-broadened half-widths of 29 lines (with J values ranging from 3 to 50 and K from 2 to 9) have been measured in the P- and R-branches of the v 3 parallel-type band of CH 3 35Cl. These lines, located in the spectral range 684–767 cm -1, were recorded using a tunable diode-laser spectrometer. The collisional half-widths were estimated along with line strengths by fitting Voigt profiles to the measured shapes of the individual lines. The results obtained for line strengths are generally larger than those derived from previous measurements.

Absolute intensities and foreign gas broadening coefficients of the 11 1,10←11 2,10 and 18 0,18←18 1,18 lines in the v7 band of C 2H 4

Absolute intensities and foreign gas broadening coefficients of the 18 0,18←18 1,18 and 11 1,10←11 2,10 transitions in the v 7 band of C 2H 4 near 948 cm -1 have been measured at a spectral resolution of ∽5 × 10 -4cm -1 using tunable diode laser spectrometry. Ar, He, N 2, and O 2 were used as the broadening gases. In order to determine the temperature dependence of the broadening coefficient, data were obtained at temperatures ranging from 150 to 296 K. The absolute intensity of the 5 0,5←5 1,5 transition was also found at 296 K. A band strength of 339 ± 10 cm -2atm -1 was obtained from weighted averages of the individual line intensities and a rigid asymmetric top calculation.

Analysis of the High-Resolution Spectrum of Ammonia (14NH3) in the Near-Infrared Region, 6400-6900 cm−1

The near-infrared absorption spectrum of 14NH3 covering the 6400-6900 cm−1 region has been obtained at a resolution of 0.005 cm−1 using a Fourier transform spectrometer. The spectrum is very complex, with many squeezed or blended lines which cannot be resolved even by Doppler-limited spectroscopy. A total of 1710 lines have been observed, and 381 rotational-vibrational transitions have been assigned to the combination band v1 + v3 and the overtone band 2v3.

Infrared Observations of Methanol in Comet P/Swift-Tuttle

We present infrared spectroscopic observations of Comet P/Swift-Tuttle obtained with the Cryogenic Spectrometer at Kitt Peak on 1992 November 8, 9, and 12 and December 8 and 10. The spectra cover the 2.9-3.6-μm region. We detect emission from the v3 band of cometary methanol at 3.52 μm in all of our spectra. During this time, the production rate of methanol was QCH3OH = 2-6 × 1028 sec-1, with weak evidence for short-term temporal variability in QCH3OH. We find the weighted average for the relative abundance of methanol with respect to water to be 7 ± 1%, which supports the notion that methanol constitutes a significant fraction of the volatile carbon in comets. Our spectra of Comet P/Swift-Tuttle indicate that the v2 and v9 bands of methanol comprise approximately 60% of the "cometary organic feature" centered near 3.4 μm. Formaldehyde was not detected in these spectra; upper limits are presented.

Absolute Intensities of Spectral Lines in the Q-Branch of the CH3D at Low Temperature

Abstract We report the absolute intensities of 38 lines of the Q branch of the v2 band of CH3D near 2200 cm−1, obtained at 98.3 K, using a Fourier Transform spectrometer with a resolution of 0.006 cm−1

Intensities and broadening coefficients for the Q branch of the 4 v2↔ v1 + v2 (471.511 cm -1) band of CO 2

Absolute intensities for the Q-branch of the 4 v 2↔ v 1+ v 1 2 (20003-11101) band in CO 2 have been measured for the first time. Measurements were performed for lines Q 10 to Q28, at temperatures ranging from 385 to 426 K, for pressures from 3 to 40 torr, using our long wavelength tunable diode laser spectrometer. The combination of tunable diode lasers, a White cell, and a blocked impurity band detector enabled us to obtain signal to noise ratios #62;1000 in the 471 cm -1 spectral region, with ∼3×10 -4 cm -1 spectral resolution. The band strength was found to be 8.6(2)×10 -25cm molec -1 @296K, and the Hermann-Wallis factor was determined. Comparison with the values listed in the HITRAN 92 database are presented. Self-, N 2- and O 2-broadening coefficients were also measured.

Absorption in the Q-branch of the v1+ v2+ v3 band of O 3

We have examined line-mixing in the Q-branch of the v 1+ v 2+ v 3 band of ozone perturbed by N 2 at room temperature. Comparison between Fourier-transform and synthetic spectra has shown that the effect of line-mixing can be neglected in the computation of atmospheric spectra in the spectral region under investigation.

Self broadening in the v1 band of NH 3

Self-broadening coefficients, pressure shifts and integrated intensities have been measured for Q- and R-branch transitions in the v 1 fundamental band of ammonia using a difference-frequency laser spectrometer. A strong, systematic J and K dependence of the broadening coefficients, reminiscent of the ground-state inversion transitions, is observed and compared with semiclassical line broadening calculations. Dicke narrowing is evident at intermediate pressures for the sharpest lines, primarily the R( J, 0) transitions. Incipient line mixing is apparent in the Q branch at pressures above ∼0.1 bar.

High-resolution IR study of the NCCCH-CO complex

The high-resolution IR spectrum of the NCCCH-CO van der Waals molecule has been investigated. The v1 band of the complex has been recorded, analyzed and accurate molecular constants were obtained. The H-C hydrogen bond length was determined to be 2.615 Å assuming that the structures of the two monomers remain unchanged upon complexation. An analysis of the rotational state dependence of the spectral lineshape allows us to obtain the predissociation lifetime of the complex and to establish the presence of intramolecular coupling enhanced predissociation at J = 8 level and around J = 22 of the v1 = 1 state. Finally, the results obtained here for OC-HCCCN are compared with similar results obtained for OC-HCN in other laboratories.