Absorption Bands Ν1 Research Articles

Laser spectroscopy of the ν1+3ν3 absorption band in C212H2. I. Pressure broadening and absolute line intensity measurements

We have developed a Ti:Sa autoscan laser spectrometer and used it to perform a detailed investigation of individual line profiles in the ν1+3ν3 band of C212H2. Pressure self-broadening effects were measured for most lines with J″ values ranging from 0 to 22, and for pressures between 10 and 600 Torr. The high-pressure data points (p>250 Torr) are fitted satisfactorily by a Voigt profile. Line narrowing, characterized by an underestimation of the Lorentz contribution to the Voigt profile, was observed for the low pressures range (p<150 Torr), indicating the influence of molecular confinement. The two usual limit models (soft and hard collisions) were fitted to the observed line shapes in order to extract more precise information concerning the pressure broadening. The present results confirm the absence of strong vibrational dependence in the self-broadening coefficients. Absolute line intensities are also determined in the fitting procedure. No significant differences were found for the two pressure domains if the appropriate model in each range is used.

Temperature evaluation of UF 6 and cluster detection in nozzle expansion using low-resolution infrared absorption spectroscopy

and mixtures of UF6 with argon and nitrogen through a bidimensional nozzle was studied using low-resolution infrared spectroscopy in the ν3 absorption band region. The experiments were carried out in order to calculate the molecular temperature of the beam and also to verify cluster formation in the expansion. The molecular beam temperature evaluation was based on the measurements of the low-resolution bandwidth, which were compared to simulated spectra results. The temperatures were also evaluated using the measured pressure at the end of the nozzle by a pitot tube. In the conditions where no cluster formation was observed the calculated theoretical temperatures using an equilibrium expansion model are in good agreement with the data obtained through the analysis of the experimental spectra and through the pitot tube pressure measurement. Cluster formation was observed for temperatures below about 120 K. In these conditions the infrared spectra showed shoulders in the region above 630 cm-1 and a shoulder or band between 616 and 600 cm-1.

Emissive characteristics of mesa-stripe lasers (λ=3.0–3.6 μm) made from InGaAsSb/InAsSbP double heterostructures

The directional patterns, current-voltage characteristics, and spectral characteristics of mesastripe lasers with InGaAsSb active layers, emitting at λ=3.0–3.6 μm (77 K) and having threshold currents ≥15 mA (jth≥200 A/cm2), are investigated. The maximum output power is 1.4 mW (λ∼3.3 μm), the differential quantum efficiency ∼3%(τ=5–30 μs, f=500 Hz) for lasing in a longitudinal mode with beam divergences ΔΘ∥∼15° and ΔΘ ⊥ ∼30°. The relationship of the differential quantum efficiency to the order of the spatial mode of the lasing is demonstrated. A single-mode, current-tunable (−30 cm−1/A) laser is used to measure the transmission of methane in the region of the ν3 absorption band.

High-Resolution Fourier Transform Spectra of HDS in the Regions of the Bands ν1and 2ν1/ν2+ ν3

High-resolution spectrum of the HDS molecule was recorded with the Bruker Fourier spectrometer in Oulu in the regions of the ν1and 2ν1/ν2+ ν3absorption bands. Fine rotational structure of the ν1band was analyzed with the model of an isolated vibrational state, while in the analysis of the 2ν1and ν2+ ν3bands it was necessary to take into account the resonance interactions between these two bands. Comparison of the experimentally determined parameters is made with the deductions of the expanded local mode approach.

Infared spectroscopic, x-ray, and nanoscale characterization of strontium titanate thin films

Attenuated total reflectance (ATR) measurements were performed using Fourier transform infrared (FTIR) spectroscopy in the ATR mode with a thallium iodobromide (KRS-5) crystal to measure the frequencies of the ν3 and ν4 phonon absorption bands in thin strontium titanate films deposited on single-crystal yttriumbarium copper oxide (YBCO), lanthanum aluminate, magnesium oxide, and strontium titanate substrates. The KRS-5 crystal enabled FTIR-ATR measurements to be made at frequencies above 400 cm−1. Atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements were also made to further characterize the films. The measurements were repeated on single-crystal specimens of strontium titanate and the substrates for comparison. Softening in the frequency of the ν4 transverse optical phonon in the lattice-mismatched films below the established value of 544 cm−1 is indicative of the highly textured, polycrystalline ceramic nature of the films and is consistent with the XRD and AFM results.

Analysis of the ν1 and ν3 absorption bands of 32S 16O 2

The spectrum of 32S 16O 2 between 1055 and 2000 cm −1 has been investigated under high resolution with a Fourier transform interferometer. Two fundamental bands have been analyzed; the A-type band ν 3 and the B-type band ν 1. A careful analysis of these bands has led to the availability of an extended and more precise set of rotational levels belonging to the vibrational states (000), (100) and (001). From this set of improved vibrational energies, rotational and centrifugal constants for the states (000), (100), and (001) have been obtained.

Dependence of fluorescence from laser irradiated SiF4 on the CO2 laser wavelength

The energy per unit urea necessary for the occurrence of visible fluorescence from dissociation products of laser irradiated SiF4 has been measured for several values of CO2 laser wavelength and gas pressure. Fluorescence was observed at a lower irradiance when the laser was tuned far from the ν3 absorption band of SiF4 than when the laser was coincident with the absorption band. In the latter case the irradiance required for dissociation decreased as gas pressure was increased from 2 to 10 Torr. However, for nonresonant excitation the irradiance required increased with increasing pressure in the same pressure range. In addition the temporal response of the fluorescence to the exciting radiation was found to depend upon the laser wavelength.

Infra-red spectra of CO2 adsorbed on evaporated alkali halides

The infra-red spectrum of CO2 adsorbed on high-surface-area films of evaporated alkali halides has been investigated at different temperatures and surface coverages. The ν3 vibration has been obtained as a sharp, strong, single band. For NaCl and NaI films, the ν2 vibration always appeared as a well-resolved doublet. Possible reasons for the appearance of the doublet are discussed, the most acceptable being the removal of degeneracy in the adsorbed state. For CsCl and CsI, the ν2 doublet appeared at higher surface coverages only. The possible relation between the spectrum observed and the crystalline structure of the substrate is discussed. From the shape and temperature independence of ν2 and ν3 absorption bands it is concluded that, in the system studied, no rotation exists in the adsorbed state.

Infrared Band Shapes and the Rotational Freedom of Methyl Bromide adsorbed on Porous Glass

AbstractA study has been made of the parallel and perpendicular infrared absorption bands ν1 and ν4 of methyl bromide physically adsorbed on porous glass at a surface coverage of about 0.5, and at the temperatures of 293 and ˜ 78°K. The sharpness of the ν1 band at room temperature as compared with the same band in the gas phase shows that free rotation about axes perpendicular to the 3‐fold molecular axis does not occur in the adsorbed state; this is probably because of hydrogen bonding between surface OH groups and the bromine atoms. However, in the adsorbed state at room temperature ν4 retains much of the width of the gas‐phase band, and on cooling to low temperatures it becomes markedly narrower, approximately to the extent expected if rotation about the 3‐fold molecular axis remains essentially free. The behaviour at low temperature is inconsistent with a hypothesis which would explain the room‐temperature band‐width as being caused by partial splitting of the vibrational degeneracy.