Vibrational spectra of a GaS single crystal

The Raman and infrared active long wavelength phonons of a GaS single crystal were studied at different temperatures in the 10–600 cm^?1 range. Properly polarized Raman spectra could be obtained with the 4880 Å exciting line and the previous assignment of the E_1g modes controversed recently could be confirmed. Infrared spectra were recorded in the 30–600 cm^?1 region. The vibrational frequencies of the crystal were also calculated using a method developed by Wieting and six new frequencies corresponding to infrared and Raman inactive modes have been proposed.We have observed that the degree of leakage of scattered intensity in unallowed polarizations increases when the wavelength of the exciting line moves off the exciton absorption front. The phonon at 74 cm^?1 was particularly sensitive and the question of the antiresonant behaviour of this compound is raised.     

The submillimeter-wave spectrum and spectroscopic constants of SO2 in the ground state

The submillimeter-wave spectrum of SO₂ has been recorded with 0.004 cm^?1 resolution in the region 8–90 cm^?1. About 2000 lines were observed, 1500 of which have been assigned to the ground state rotational transitions of ³²SO₂. Molecular constants up to the 10th order have been derived, combining our data with the available microwave data in the literature. SO₂ rotational spectrum line positions up to 90 cm^?1 can be reproduced from these constants, within the experimental accuracy (2 × 10^?4 cm^?1).     

Comparison of band model and integrated line-by-line synthetic spectra for methane in the 2.3 μm region

The 2.3 μm spectral region of methane can be used to retrieve cloud properties of planetary spectra, provided parameters for the methane spectrum are known. Two standard techniques for calculating absorption spectra in this region are compared here. A Voigt profile Mayer-Goody random band model is applied, using coefficients empirically fitted by Fink et al. to CH₄ spectra recorded with high absorping amounts at 10 cm^?1 resolution. Calculation of the absorption is also done with a line-by-line direct integration method for the same gas conditions using molecular parameters obtained by combining an older unpublished list of observed positions and estimated line strengths (derived from 0.04 cm^?1 resolution data) with quantum assignments from the literature. The molecular parameters have been evaluated for the 4180–4590 cm^?1 region by comparing new laboratory spectra with 0.01 cm^?1 resolution recorded at 296 and 153K with synthetic spectra calculated at the same conditions. The deficiencies of the molecular parameters and random band coefficients for this spectral region of CH₄ are then discussed qualitatively and demonstrated by comparing 10 cm^?1 resolution synthetic spectra calculated by both methods for the same gas conditions at 296, 153, and 55 K.Curves of growth of the total equivalent width are calculated at 296 and 55K for a pathlength of 50 cm and pressures up to 10 atm. Changing the mean line spacing in the band model gives better agreement between the spectra calculated by the two techniques at low gas temperatures. The required multiplier has been determined for the mean line spacing for pressures from 10^?6 to 10^?1 atm at 55, 100, and 150 K.     

Experimental (UV,NMR, IR and Raman) and theoretical spectroscopic properties of 2-chloro-6-methylaniline

In this work, the experimental and theoretical UV, NMR and vibrational spectra of 2-chloro-6-methylaniline (2-Cl-6-MA, C₇H₈NCl) were studied. The ultraviolet absorption spectra of compound that dissolved in ethanol were examined in the range of 200–400 nm. The ¹H, ¹³C and DEPT NMR spectra of the compound were recorded. FT-IR and FT-Raman spectra of 2-Cl-6-MA in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies were found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the calculated NMR chemical shifts and absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Laser-induced Raman scattering in calcium titanate

The Raman spectrum of polycrystalline calcium titanate prepared by a liquid mix technique and heated to 800°C has been recorded at room temperature using an argon-ion laser as exciter. The observed spectrum was interpreted on the basis of factor-group C_2V. Not all of the Raman active modes predicted by factor group analysis were observed and this could be due to: over-lapping of bands, or very low polarizabilities of some of the modes or masking of the weak bands by intense bands. The band at 639 cm^?1 is tentatively assigned to the TiO symmetric stretching vibration (γ₁) and the bands at 495 and 471 cm^?1 to torsional modes. The bands in the region 180–340 cm^?1 are assigned to the OTiO bending modes and the 155 cm^?1 band to the Ca(TiO₃) lattice mode. The observed Raman bands are compared with the available infrared absorption data and, as expected, some coincidences in frequencies are seen for this compound with a noncentrosymmetric structure.     

The vibration-rotation HDO absorption spectrum between 8558 and 8774 cm−1

The absorption spectrum of HDO has been recorded in the region 8558–8774 cm^?1 using a high-sensitivity intracavity F₂^?:LiF center laser spectrometer. The absorption sensitivity is 10^?7 cm^?1 and the line-center determination accuracy is about 4 × 10^?2 cm^?1. The spectrum was interpreted and the absorption lines were attributed to the ν₂ + 2ν₃ band of HDO. Energy levels up to J = 12 and rotational and centrifugal parameters of the vibrational (012) state were obtained.     

The Electronic Absorption Spectrum of Hafnium Monochloride

Abstract

Intracavity laser spectroscopy has been applied for investigation of absorption spectrum of HfCl molecule. In the region 560–700 nm 59 bands have been obtained. Rotational structure analysis of 0–0 band indicated that Hund's case (c) of angular moment coupling applied to this molecule. The molecular constants (cm^?1) calculated for upper and ground electronic states are: ω′ = 353.05 cm^?1, ω″ = 379.65 cm^?1, B′=0.21486 cm^?1 B″ = 0.21801 cm^?1.     

Structure comparison of Orpiment and Realgar by Raman spectroscopy

Raman spectroscopy was used to characterize and differentiate the two minerals, Orpiment and Realgar, and the bands related to the mineral structure. The Raman spectra of these two minerals are divided into three sections: (a) 100–250?cm^?1 region attributed to the sulfur–arsenic–sulfur bending vibrational modes; (b) 250–450?cm^?1 region due to the arsenic–sulfur stretching vibration; and (c) 450–850?cm^?1 region assigned to overtone and combination bands. A total of 14 Raman bands for the spectrum in the 1600–100?cm^?1 region were observed. The significant differences between the minerals Orpiment and Realgar are observed by Raman spectroscopy. Realgar shows the typical bands observed at 340, 268, 228, and 218?cm^?1, and the special bands at 379, 289, 200, 176, and 102?cm^?1 for Orpiment are observed. The additional bands in 850–450?cm^?1 region are only observed for the mineral Orpiment, which may be attributed to overtone and combination bands in the Raman spectrum. The variation in band positions is dependent upon the structural symmetry, arsenic–sulfur bond distances, and angles. Moreover, another cause for the difference is the effect of the intermolecular forces and to the strong coupling between close lying external and internal modes. The difference of these two minerals structure induce tremendous diversity on Raman spectra, so Raman spectroscopy offers the information on the molecular structure of the minerals Orpiment and Realgar.     

The dependence of muon intensity on the geomagnetic latitude

The vertical momentum spectrum of cosmic-ray muons has been determined by a counter controlled neon-hodoscope in the spectral region (0.2–3) Bev/c at geomagnetic latitude 12 °N. The observed spectrum agrees satisfactorily with the calculated spectrum of Olbert for muon momentum above 1.8 Bev/c. Below about 1.8 Bev/c, the measured spectrum exceeds slightly the theoretical spectrum of Olbert, calculated for the same geomagnetic latitude. The measured spectrum agrees with the experimental spectrum of Allkofer at 9 °N, but is somewhat below the spectrum obtained by Hayman in the low momentum region at 57.5 °N. This shows that there exists a latitude dependence of the low momentum muon spectrum. The estimated integral intensity of muon of momentum ≧320 Mev/c is found to be 7.3×10^?3 cm^?2 sec^?1 str^?1 which agrees with the value of other investigators^1–9.     

Scaled Quantum Chemical Studies of the Molecular Structure and Vibrational Spectra of Minoxidil

The Fourier transform Raman and Fourier transform infrared spectra for minoxidil have been recorded in the region 4000—100 cm^?1 and 4000—450 cm^?1, respectively. The structural and spectroscopy data of the molecule in the ground state were calculated by using density functional theory methods with 6-311G (d, p) basis set. A detailed vibrational analysis of the title compound has been done using normal coordinate analysis following the scaled quantum mechanical force field methodology. The calculated molecular geometry parameters and scaled vibrational wavenumbers are well compared with the experimental data. The electronic properties, such as excitation energies, absorption wavelength, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energies were performed by time-dependent density functional theory approach, and the results are in good agreement with experimental absorption spectrum. The charge delocalizations of these molecules have been analyzed using natural bond orbital analysis. The molecule orbital contributions are studied by density of energy states. Fukui functions, local softness, and electrophilicity indices for selected atomic sites of the title compound are determined. Finally, the thermal behaviors of the compound have been calculated by different temperature.     

The ν9 band of diazirine,H2CN2, by Doppler-limited Fourier transform infrared spectroscopy

The Doppler-limited infrared spectrum of diazirine was recorded using a high-information Fourier transform spectrometer with a resolution of 0.0054 cm^?1. The rovibrational structure of the ν₉ fundamental (CH₂ rocking) at 1124.9144 cm^?1, which is a C-type band, was analyzed in detail with extensive use of spectrum simulation and correlation diagrams. The molecular constants for the upper energy level of this band were obtained from the overall rovibrational assignment of more than 2000 transitions, which cover the region from 1070 to 1220 cm^?1.     

High resolution vibration-rotation spectra of carbon suboxide: Molecular constants for the ground state and 2ν70

The infrared spectrum of C₃O₂ was recorded with the vacuum Fourier transform interferometer of Laboratoire Aimé Cotton at a resolution of 0.005 cm^?1. The ground state molecular constants were calculated from lower state combination relations in a simultaneous analysis of six ground state transitions situated in the region 3000 to 5000 cm^?1. Through the analysis of a difference band we established that $\text{2ν}{}_7{}^0$ is 60.7022 ± 0.0005 cm^?1 above the ground vibrational state. Accurate molecular constants were also determined for this vibrational level.     

Absorption spectrum of trideuteromethane between 7 and 11 μm. Analysis of the ν5 band

The absorption spectrum of trideuteromethane was recorded in the range 900–1400 cm^?1 with a resolution of 0.020–0.025 cm^?1. The ν₅ band centered at 1292.499 cm^?1 is analyzed here. A fit based on 869 observed transitions including J′ values up to 22, leads to a set of spectroscopic constants suitable for energy calculations in the upper-state v₅ = 1. These constants reproduce the experimental wavenumbers with a standard deviation equal to 0.008 cm^?1. The tabulated line strengths are calculated on the basis of the value S = 27.1 cm^?2 atm^?1 at 300 K, measured by Hiller and Straley, for the band strength of ν₅. A useful comparison is made between the values now derived for some constants and the corresponding ones predicted by Gray and Robiette in their recent force field calculations of methane and isotopic species.     

High resolution infrared spectrum of silane

The infrared absorption spectrum of SiH₄ in the 4200–4500 cm^?1 region has been recorded using a high resolution grille-spectrometer. Two bands have been observed and identified as 2ν₃ and ν₁ + ν₃. Some molecular constants have been calculated, using the formalism developed by Jacques Moret-Bailly.     

Terpenes in the gas phase: The Far-IR spectrum of perillaldehyde

The far infrared spectrum of S-(-)-perillaldehyde, a monoterpene containing an aldehyde functional group, has been recorded in the gas phase using FTIR spectroscopy. The vibration signature of the three most populated rotamers has been observed and identified in the 30–650 cm^?1 range. The vibration assignment was based on the scaled B3LYP/cc-pVDZ harmonic force field of Partal Ureña et al., 2008 [10]. Anharmonic contributions calculated at the HF/6–31+G^? level were found negligible.     

Line strengths of the ν1 + ν4 band of 12CH4

The line strengths of the ν₁ + ν₄ band of ¹²CH₄ at 4223.5 cm^?1 were measured using a leastsquares procedure that iterates between the observed spectrum and a synthetic spectrum calculated at correct instrumental and gas sample conditions. The methane spectrum was recorded at 0.011 cm^?1 resolution with signal-to-noise ratios of 300 to 1 or better using a Fourier transform spectrometer at Kitt Peak National Observatory. Line assignments were evaluated and extended to upper state J of 13. The observed line strengths reflect significant perturbation by other states so that only portions of the band can be used to determine a band strength of 6.92 (2) cm^?2 atm^?1 at 296 K with a Herman-Wallis factor of (1 – 0.0035(2)m)².     

Photo-absorption studies on carbonyl sulphide in 30,000–91,000 cm−1 region using synchrotron radiation

Photo-absorption spectrum of carbonyl sulphide (OCS) is recorded in 30,000–91,000 cm^?1 (3300–1050 Å) region at an average resolution of 1.2 Å using Photo-physics beamline on the 450 MeV Indus-1 synchrotron radiation source at RRCAT Indore, India. Owing to significant absorption cross section dependence, spectra of OCS are recorded at various pressures (0.001–5 mbar) to optimize the S/N ratio for band systems appearing at different energy regions. The spectral region below 70,000 cm^?1 has contributions from dissociation mechanism of the ground state of OCS and three valence band systems arising from promotion of a 3π electron to 4π and 10σ orbital. Improved S/N ratio helped in unambiguous assignment of the valence band progressions at 42,000–48,000 cm^?1, 53,000–62,000 cm^?1 and 63,500–70,000 cm^?1 regions to the ¹Δ←X¹Σ⁺ transition, the relatively intense and sharp bands of ¹Π←X¹Σ⁺ transition and intense but broad bands of ¹Σ⁺←X¹Σ⁺ transition, respectively, and obtain the vibrational frequencies. Above 70,000 cm^?1 Rydberg series arising from s, p, d and f orbitals converging to the ionic ground state X²Π of OCS⁺ (90,121 cm^?1) are identified. Long progression in the first few members of the Rydberg series is suggestive of mixed valence character. Quantum defects are evaluated and used to discuss the nature of the molecular orbital. The present study provides a unifying picture of the VUV photo-absorption spectrum of OCS up to its first ionization limit.     

Investigation of the water vapor emission spectrum in the region 9600–12000 cm−1

To record weak emission spectra, a high-sensitivity diffraction spectrometer, operating in the region 400–1100 nm, has been designed on the basis of a DFS-452 spectrograph and a photodiode reader with a spectral resolution of 0.14 cm^?1. A Multiplaz-2500 plasmatron, generating intense molecular emission spectra in the visible and near-IR regions, served as a source of the water vapor emission spectrum at temperatures above 3000 K. Water vapor emission spectra have been recorded for the first time in the range above 10 000 cm^?1. The analysis of the spectra obtained has shown that the plasmatron emission spectrum also includes the lines of the OH radical.     

The high-resolution spectrum of ozone between 8 and 150 cm−1

The rotational spectrum of ¹⁶O₃ in the region 8–150 cm^?1 has been measured at high resolution (0.0033 cm^?1 at 30 cm^?1) with a polarizing FT interferometer. From the rotational analysis of the present data (about 1000 transitions) combined with the previously reported millimeterwave data (about 210 transitions), a new set of rotational and centrifugal distortion constants was derived, which reproduces the measured transition frequencies within their accuracy.     

Far-infrared spectrum and ring-puckering of 3-cyclopenten-1-one

The far-infrared spectrum of 3-cyclopenten-1-one in the vapor phase has been recorded and a broad absorption with a series of several Q branches was observed in the 80–120 cm^?1 region. This series of transition frequencies resulting from the ring-puckering vibration was fitted by the single minimum potential function V = 11.31 (Z⁴ + 12.56 Z²) cm^?1, which is characteristic of a planar ring structure. The origin of the potential function for this molecule and related molecules is discussed.