V3 Band Research Articles

A direct study of the vibrational bending effect in line mixing: The hot degenerate 1110 ← 0110 transition of CO2

The study of the isotropiv Raman Q-branch of a hot band Π ← Π allows one to establish a direct connection between the vibration-rotation angular momentum coupling and the resulting spectra. Due to the l-doubling, the Q-branch is split into two subbranches characterized by either even or odd rotational quantum number j. The vibrational bending reduces the rotational transfer rates inside each of these subbranches by a factor of about two and induces an inter-subbranch coupling. The expected propensity rule towards conservation of the parity index for high rotational levels is well observed. Calculated spectra are in excellent agreement with CARS experiments for the v1 + v2 ← v2 band of CO2.

N 2 and Ar broadening and line mixing in the P and R branches of the v3 band of CH 4

N 2- and Ar-broadened spectra of the allowed P- and R-branch manifolds for J ⩽ 10 in the v 3 band of CH 4, have been recorded from the Doppler limit to ∼ 67 kPa at T = 295 K using a tunable difference-frequency laser spectrometer. The broadening coefficients exhibit larger variations among the tetrahedral components in the R-branch manifolds than in the P branch, which in turn are very similar to the Q branch previously measured [A.S. Pine, J. Chem. Phys. 97, 773 (1992)]. The broadenings for Ar are uniformly 88(1)% of those for N 2. Line intensities, pressure shifts and Dicke narrowing coefficients are also obtained. Strong line mixing among the blended tetrahedral components is observed, and an analysis is presented restricting line coupling among transitions with the same nuclear spin A, E or F symmetry with the sum of the mixing coefficients for a given symmetry in a J manifold constrained to zero.

Improved Infrared Spectroscopic Method for the Measurement of 13C: 12C Ratios

Pressure broadening of an infrared absorption band of gaseous CO2 makes measurement of a band intensity very much easier and also much more precise in comparison with the results obtained by measuring the intensity of a single line in a gas-phase spectrum. The isotopic shift of the v3 bands for carbon dioxide centered at 2350 cm−1 is sufficient to completely separate the P branch for 13CO2 from the two branches for 12CO2. The intensity ratios can be measured accurately on a low-resolution FT-IR spectrometer when the CO2 is pressurized to 10 bar (106N m−2) with N2, permitting isotope ratio differences as small as 0.02 atom % above the natural abundance of 1.11 atom % to be detected.

Improved Curve Resolution of Highly Overlapping Bands by Comparison of Fourth-Derivative Curves

Curve fitting of highly overlapping bands can be improved by comparison of the fourth derivative of the experimental composite band profile with that of the sum of the curve-fitted component bands. Optimization is achieved with fixed values of one band parameter, aiming thereby for optimal correspondence between the fourth-derivative curves. FT-IR spectra of nitrate's v1 band region in ≈1 M glassy Ca(NO3)2 solution, and of its v2 band region in 10 M LiNO3 solution, in ≈0.5 M glassy Mg(NO3)2 solution and in 5 M Ca(NO3)2 solution, all with D2O as solvent, were used. As a general rule, reliable curve fitting of two overlapping bands of unknown band shape is possible only when separation of their peak maxima is larger than their average full width at half-height (FWHH). We show here that by comparison of fourth-derivative curves many more overlapped composite bands can be reliably resolved into their component bands, and, for the favorable case of 10 M LiNO3 solution, separation of two bands by only about a third of their average FWHH is sufficient for reliable curve fitting. This method requires data with very high signal-to-noise ratios. Improved curve fitting of highly overlapping bands is demonstrated for both a sum and a product of Gaussian and Lorentzian peak shapes, and a sort of recipe is given for both types of curve fitting. Synthetic spectra of two overlapping bands, where the degree of overlap and their relative intensity were varied in a systematic way, are given together with their fourth-derivative curves. This information will be of help for interpreting fourth-derivative curves of experimental highly overlapping two-band systems.

Absolute line intensities in the v3 band of 12CH 3F at 9.6 μm

Infrared absolute line intensities of the v 3 band of 12CH 3F have been measured around 9.5 μm using a diode-laser spectrometer. We have deduced the vibrational band-strength to be S 0 v = 377.9 ± 5.9 cm −2 atm −1 at 296 K and the first Herman-Wallis factor.

Diode-laser measurements of N 2- and O 2-broadening coefficients in the v3 band of CH 3D

Using a tunable diode-laser spectrometer, N 2- and O 2-broadening coefficients have been measured in the Q P and Q R branches of the v 3 band of 12CH 3D. The collisional widths have been obtained by fitting Voigt and Rautian profiles to the measured shapes of the lines. Semi-classical calculations of the broadening coefficients have shown the importance of the non-electrostatic contributions in the anisotropic intermolecular potential.

Rotational analysis of the v1(a′) band at 3325.42 cm −1 of the mid-infrared spectrum of C 2H·CDO

The mid-infrared spectrum of the v 1(a′) band at 3325.42 cm −1 of the deuterium substituted propynal molecule C 2H·CDO was recorded at a resolution of about 0.08 cm −1. A detailed analysis of the partially resolved band was completed using computer simulation techniques leading to the derivation of the values for the changes in the rotational constants on excitation (A″-A′), (B″-B′) and (C″-C′).

Line-mixing effects in the 3 v3 band of CO 2 perturbed by Ar

Measurements of absorption coefficients in the 3 v 3 band of CO 2 at 1.44 μm perturbed by Ar up to 146 bar have been analyzed by using two line-mixing theoretical calculations within the impact approximation. In the first approach, the relaxation operator is treated semi-classically with adiabatic corrections. In the second, the relaxation operator is modelled with the Energy Corrected Sudden (ECS) approximation associated with a power fitting law providing the basic rotational state-to-state rates. Although the line-coupling spectroscopic cross-sections of the two models are significantly different, they both lead to satisfactory agreement with bandshapes at moderate densities (< 100 Amagat). Significant deviations between experimental and calculated spectra appear at higher densities. They are mainly attributed to the probable breakdown of the impact and binary collision approximations and to a number of reasons including an incorrect ECS calculation of the interbranch coupling, the nonlinear density dependence due to the finite volume of the molecules, and the neglect of the unknown imaginary part of the off-diagonal elements in the calculated relaxation matrix.

High resolution FTIR spectrum of the v1 band of bromochloromethane

The IR spectrum of the v 1 band of natural bromochloromethane (CH 2BrCI) has been recorded at a resolution of 0.008cm −1 in the region 2940–3060 cm −1 on a BOMEM DA3.002 Fourier-transform spectrometer. The rovibrational analysis on the strong Q branch of this B-type band has been performed in the prolate symmetry top approximation due to the fairly small difference between constants B and C. A normal linear least-square fitting of the identified P, R Q K ( J) clusters provided the corresponding excited state molecular parameters for three of the four naturally existing isotopomers of bromochloromethane with a standard error of about 0.02 cm −1.

Intensities of the 1397 cm −1 ( v3) band of HO 2NO 2 and feasibility of atmospheric detection

Absorption coefficients of the 1397 cm −1 ( v 3), band of peroxynitric acid (HO 2NO 2) have been measured at 225–230 K in order to calculate the feasibility of detecting this spectral feature in atmospheric spectra. High-resolution (0.0078 cm −1) Fourier transform spectra (1370–1430 cm −1) of low pressure gas-mixtures containing HO 2NO 2 were analyzed to determine the absorption coefficient k(v). The maximum absorption coefficient was found to be 1.0 × 10 −18 cm 2/molec at the peak of the 1397 cm −1 Q-branch. An average pressure broadening coefficient of 0.1 (± 0.02) cm −1/atm was also measured using a tunable diode laser spectrometer (resolution 0.001 cm −1) and a convolution technique. The high resolution spectrum and pressure broadening coefficient were used to simulate the atmospheric transmission spectrum at an altitude where HO 2NO 2 is expected to have its peak in the vertical concentration profile (27 km).

Ab Initio Calculations of the Excited States of Formamide

The excited states of formamide in the gas phase have been calculated using multireference configuration interaction methods. The nπ* transition is calculated to be at 5.85 eV, and the ππ* transition is placed at 7.94 eV. The corresponding experimental energies are 5.65 and 7.32 eV, respectively. In addition, a number of states with significant intensity are calculated to occur in the region of the experimental spectrum designated as the V1 band. The experimental ππ* transition dipole moment, 3.71 D, is estimated by assuming that the intensity of the V1 band is due solely to the ππ* transition. The calculated ππ* transition dipole moment is 3.70 D, if only one unoccupied a‘‘ orbital is included in the active space. If the number of unoccupied a‘‘ orbitals in the active space is increased, the calculated ππ* transition moment drops to 2.40 D, and another transition, the π3pπ, appears at 7.40 eV, but with only low to moderate intensity. The calculated orientation of the ππ* transition dipole moment agrees w...

The structure of the V centre produced by KrCl excimer laser irradiation of KI crystals at low temperatures

KrCl excimer laser irradiation (hv = 5·58 eV) of KI single crystals at about 150 K produces F, F′, α, β and V centres. The V centres give rise to V2 and V3 bands which exhibit <100>-type dichroism. In KI crystals containing the V centres, the 111 cm-1 Raman line originating in the symmetric stretching vibration mode of an I- 3 molecular ion appears. On the basis of the I- 3 molecular ion model for the V centre, the V2 and V3 bands are considered to be due to relatively stronger transitions from the ground 1Σg0(σ2 uπ4 uσ2 gπ*4 u) state to the excited 1Σu0(σ2 uπ4 uπ4 gσgπ*4 uσ*u) and 3Πu0(σ2 uπ4 uπ3 gσ2 gπ*4 uσ*u) states respectively. The splitting of these two bands is ascribed mainly to the spin-orbit interaction. The deviation from a linear array of the I- 3 molecular ion bound by a cation vacancy is discussed from the experimental viewpoint of Raman scattering and optical absorption.

Non-Detection of Hydrogen Cyanide on Jupiter

High spectral resolution observations of Jupiter performed at the NASA/Infrared Telescope Facility near 13.5 μm are presented. Two spectral ranges including the R(7) and R(11) lines of the v2 band of HCN were observed at high signal-to-noise. No evidence for HCN absorption in excess of 2% of the continuum was found, in contrast to the report by Tokunaga et al . (1981, Icarus 48, 283-289). An upper limit on the tropospheric HCN mixing ratio of 1 × 10-9 was derived, assuming a uniform value up to the tropopause. When HCN condensation in the upper troposphere is taken into account, only a looser upper limit around 1.2 × 10-8 can be set on the deep mixing ratio. The lack of emission cores at the position of the HCN lines provides an upper limit of 2 × 10-4 cm-amagat on the HCN column density in the stratosphere (corresponding to a maximum average mixing ratio of 8 × 10-10 above condensation level). A critical reanalysis of Tokunaga et al.'s observations is finally presented, leading to the conclusion that the previously reported detection of HCN is questionable.

Laboratory Infrared Spectra (2.3-23 μm) of SO 2 Phases: Applications to Io Surface Analysis

Mid-infrared spectra (∼2-25 μm) of various SO 2 phases (some known to be present on Jupiter's satellite Io) contain diagnostic band features that can be used with observational data of Io to learn about its surface and atmospheric composition. A key portion of this spectral range (2-5 μm) will be accessible to the Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft now headed for Jupiter. Our lab work provides reflectance spectra of SO 2 phases for: (1) comparison with IR spectra of Io, (2) identification of compositional species on Io, and (3) mapping the spatial distribution of SO 2 phases on Io. Spectra at 4 cm -1 resolution were measured for a variety of phase states of SO 2 including SO 2 gas, SO 2 frost, SO 2 slab ice, SO 2 liquid, and adsorbed SO 2. Detailed lab spectra and band identifications including some new identifications are given for several varieties of each of these phases with particular emphasis on the 2- to 6-μm regions. We also produced a variety of surface textures for condensed SO 2, ranging from frosts with many peculiar (reticulated) textures to solid slab or glaze ice and liquid. The different frost textures result from different growth conditions (such as temperature, pressure, gas-supply rate, and substrate composition). All the optically thick frosts and ices that we produced have reflectance spectra that are essentially identical, regardless of texture. Previously reported IR spectra of solid SO 2 in other investigations were usually produced as transmission spectra of films of ice, not reflectance spectra of frost or ice surfaces. Our work shows that transmission spectra of thin films are not adequate to represent all features that may be present in reflectance spectra of macroscopic frost or ice on planetary bodies like Io; this is because thin-film samples provide optical pathlength insufficient to produce detectable absorption bands at wavelengths where bands are strong in reflectance spectra of optically thick deposits (or in transmission spectra of thick (few millimeters) monocrystals). Reflection spectra, as opposed to transmission spectra, also allow easier simulation of frost thickness effects and better reproduction of hand shapes that will actually be observed in planetary spectral observations. Our results indicate that one can estimate phase state and concentration level for condensed SO 2 on Io using the principal band ( v1 + v3) in the 4-μm region; for example, we found that the v1 + v3 band-minimum position is dependent on: (a) phase state of the SO 2, (b) thickness of frost or ice, and (c) instrument resolution. SO 2 ice or frost thickness (on a millimeter scale or less) can also be assessed by the 4-μm band shape characteristics and by the presence or absence of several other weaker bands; we have done this for In spectra and find that significant fractions of In must be covered by thick (>2 mm) frost. We have successfully used our lab spectra to identify and assign new hands in Io observational data reported previously by other researchers. We developed NIMS-equivalent spectra of various SO 2 phases showing what NIMS should "see" on Io at various spectral sampling strategies (resolutions): our lab data will provide a basis for NIMS to distinguish and map the distribution of various SO 2 phases on Io's surface and also identify such phases on other Galilean satellites if detectable quantities exist there.

Dependence on concentration and temperature of the dynamics of SO in Li2SO4, Na2SO4 and K2SO4 aqueous solutions studied by Raman spectroscopy

AbstractThe Raman spectra of the v1(SO) band in aqueous solutions of Li2SO4, Na2SO4 and K2SO4 as a function of concentration at room temperature and for fixed concentrations in the temperature range 5—85°C were studied. It was found that the molar scattering coefficient for SO is virtually independent of the concentration and temperature in the studied range. Nevertheless, the v1(SO) band shows some asymmetry on the high‐wavenumber side for Li and Na and on the low‐wavenumber side for K, which for these last two cases has not previously been reported. Moreover, the band position seems to be correlated with the sign and amount of the asymmetry as the concentration increases. On the other hand, temperature does not have a great effect on the band profile. In the case of Na and K, there is little narrowing of the band, whereas for Li there is slight broadening and an increase in the asymmetry. Quantitative analysis of these changes was performed using the vibrational correlation function. This was modelled considering the distribution of sulphate oscillators in the aqueous media as a convolution product of an unperturbed distribution by a perturbation function. This last function assumes a feedback mechanism in which the main parameters are the coupling energy and the fraction of the distribution having interactions. The dependence of these parameters and of the Gaussian and Lorentzian contributions to the band profile with concentration and temperature are discussed.

Fourier transform Raman spectroscopic study of lithium perchlorate solutions in acrylonitrile

AbstractLithium perchlorate solutions in acrylonitrile (propenenitrile), in a range of concentration between 1 and 6 molal, were studied by using Fourier transform Raman spectroscopy. The new band in the v(CN) region proceeding from the bound species Li+… (acrylonitrile)n and the modifications in the C—C stretching band were studied in detail by means of deconvolution and band‐fitting procedures. An average solvation number of ca. 2.3 was obtained without any correction for the ion pairing. The data obtained in the analysis of the perchlorate anion v1 (symmetric stretch) band allow us to quantify the concentration of the different species (free perchlorate, solvent‐separated ion pairs and contact ion pairs) present, and to obtain a more realistic solvation number for the lithium ion in acrylonitrile solutions. This solvation number was estimated at 3.0 ± 0.1.

Determination of the stratospheric organic chlorine budget in the spring arctic vortex from MIPAS B limb emission spectra and air sampling experiments

Vertical profiles of halogenated source gases, CF2Cl2, CFCl3, CHF2Cl, Cl4, and CF4, were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne version (MIPAS B) during a balloon flight launched from Esrange near Kiruna, northern Sweden (68°N) on March 14, 1992. This flight was a contribution to the balloon launch program of the European Arctic Stratospheric Ozone Experiment (EASOE) campaign. All problems encountered during the analysis of the recorded spectra are discussed in detail. These are primarily the lack of spectral data for HNO3 which interferes with the CF2Cl2 v6 band, and the strong effects attributed to the Pinatubo aerosol. As the air mass sounded by MIPAS was polar vortex air, these data supplement the results of in situ air sampling experiments, which investigated air masses outside or at the edge of the polar vortex at altitudes below 18 km during the last phase of EASOE. An analysis is made of the vertical profiles of the seven most abundant organic chlorine species (CF2Cl2, CFCl3, CHF2Cl, CCl4, CH3Cl, CH3CCl3, and C2F3Cl3) during that phase of the EASOE campaign. Mixing ratios of those organic chlorine compounds which had not been measured by MIPAS are inferred from profiles provided by air sampling experiments performed between November 30, 1991, and March 12, 1992. These profiles were adjusted to the dynamic conditions during the MIPAS observations, namely the effect of subsidence, using CF2Cl2 as a tracer. This allowed to derive the relative contributions of the organic chlorine species to the total chlorine budget of the air mass sounded by MIPAS. The results are consistent with the high ClONO2 mixing ratio of 2.6 parts per billion by volume (ppbv) observed at 18.9‐km altitude during this flight of MIPAS B.

Characterization of silicon-carbon clusters by infrared laser spectroscopy. The v1 band of SiC 4

The v 1 fundamental vibration of linear SiC 4 has been observed by infrared diode laser spectroscopy of a supersonic cluster beam. Twenty-four rovibrational transitions were measured in the spectral region of 2094.6 to 2097.1 cm −1, the rotational temperature was 10 K. A combined least-squares fit of these transitions with previously reported microwave data yielded the following molecular constants: v 1 = 2095.45806(37) cm −1, B″ = 0.051161131(52) cm −1, and B′ = 0.0509157(96) cm −1. These results are compared to vibrational spectroscopy measurements of SiC 4 trapped in a solid Ar matrix and to ab initio calculations.

Vibrational Transition Moment for the v2Band of CH3D from Spectra Between 2100 and 2350 cm−1

Abstract Absolute intensities of the v2 band of monodeuterated methane in the range of 2100–2350 cm−1 have been measured at 296.3 K by means of a Fourier Transform spectrometer at 0.006 cm−1 resolution. Together with data obtained earlier at 98.3 K we determined the rotationless transition moment |R|=(9.33×10−4±3%) Debye and the Herman-Wallis factor C=(0.0136±0.0003). We report the intensity measurements and the recalculated intensity values for both temperatures.

Raman Spectroscopic Study of the Ion Association of Lithium Sulfate Aqueous Solutions

Abstract A Raman spectroscopic study of Li2SO4 aqueous solutions as function of concentration and temperature was performed. The dynamic properties of the sulfate ions were studied by a band profile analysis of their internal modes using Fourier transform methods. This analysis reveals the perturbation of the SO4 -2 vibrations due to ionic interactions. From the v1 (SO4 -2) band profile the spectroscopic ionic association constant was calculated in the range from 5 to 80 °C. The large difference found between the values thus obtained for the association constant and the values obtained from macroscopic measurements is interpreted, assuming that Raman spectra reflect only the short-range forces acting on the ions. Using the Bjerrum equation to calculate the contribution for the long-range forces, good agreement is found between the spectroscopic and macroscopic results.