The polarized reflection and absorption spectra of perylene crystals in monomeric and dimeric forms

The electronic absorption spectra of perylene crystals in the α- and β-forms were measured by the normal incidence reflection method in the spectral region from 20 000 to 60 000 cm^?1. From the absorption spectrum polarized perpendicular to [1$\text{1}$0] axis of the α-form crystal, the bands around 24 000 cm^?1 were determined to be polarized along the long molecular axis. Two strong bands with different polarizations were observed around 50 000 cm^?1 for each of the α- and β-perylene crystals and were assigned to the transitions to the ¹B_2u and ¹B_3u states. The observed polarized absorption spectra as a whole were consistent with the theoretical results by Hummel and Ruedenberg and the reflection method was found to be suitable to the polarized absorption measurement of strong bands of crystals. The observed factor-group splittings were compared with the theoretical values, the oriented gas model being found to be applicable to the β-form crystal.     

The near-ultraviolet spectrum of diacetylene trapped in solid argon at 9 K

The absorption spectra of normal and deuterated diacetylene trapped in solid argon at 9 K were investigated in the near-ultraviolet region between 2000 and 3000 Å. The vibrational structure observed at low temperature for the band system at 2448 Å, which was previously reported by Haink and Jungen in the gas phase, and identified as a ¹Δ_u ← X¹Σ_g⁺ transition, was analyzed. A comparison between the spectra for C₄H₂ and C₄D₂ suggests some revisions in the upper-state vibrational assignments. The possibility that the upper state assumes a C_2htrans configuration of ¹A_u symmetry is examined. The matrix spectra also appear to indicate that the absorption spectrum observed at 2576 Å in the gas phase and which has been assigned to a ¹Σ_u^? ← X¹Σ_g⁺ transition may not originate in the ground state of C₄H₂.     

Effect of electron bombardment on a phase-inhomogeneous nanoscopic structure and the fundamental absorption spectrum of single-crystal CuO

The optical absorption spectra of single-crystal CuO bombarded with 5-MeV electrons exhibit reduced absorption in the region of the fundamental absorption edge at 17 eV, which corresponds to the b _1g →e _u transition with charge transfer in CuO ₄ ⁶⁻ . A simultaneous increase in absorption is observed in the middle infrared and in the region of high energies centered on 2.9 eV. The experimental results obtained are interpreted in terms of ideas on the phase-inhomogeneous nano-agglomorated structure in copper oxides that occurs as a result of the nucleation of polar centers (CuO ₄ ⁵⁻ , CuO ₄ ⁷⁻ ) under electron bombardment. Fiz. Tverd. Tela (St. Petersburg) 39, 2141–2146 (December 1997)     

Far infrared polarization measurements of MEM(TCNQ)2 at room temperature and 4.2 K

Polarization measurements have been made in the far infrared absorption spectra on single crystals of MEM(TCNQ)₂ at 1.5, 4.2 and 298 K. We demonstrated experimentally that the direction of polarization of phonons at 126 and 156 cm⁻¹ below spin-Peierls transition are parallel to the c-axis. Secondly, we measured the absorption spectra of MEMI powder at 1.5 and 4.2 K and found that there is no absorption in the range from 130 to 170 cm⁻¹. This indicates that there is no intramolecular vibration of MEM in this region. It supports the assignment of 156 cm⁻¹ absorption as phonon. Thirdly, comparing the FIR absorption spectra at 4.2 and 298 K with linearly polarized radiation field parallel to the c-axis, we found that the height of the strong absorption band observed around 86–180 cm⁻¹ region at 4.2 K becomes lower with the raising of temperature to 298 K. We attributed this band to the pinned CDW. The lowest edge of the CDW is 70 cm⁻¹.     

Vibrational mode of polaron in trans-(CH)x

The vibrational frequency of polaron configuration in trans-(CH)_x is calculated, and we find the obtained wavenumber v_p = 578 cm^?1 coincides with the observed feature of the infrared absorption spectra at the region of 500–600 cm^-1.     

Infrared spectroscopy of a dense potassium vapor jet

In this paper we report the development of new apparatus for the containment and study of dense alkali metal vapors, and the use of the apparatus to study the infrared spectra of potassium vapor. The apparatus is the first to employ aerodynamic confinement of a dense alkali vapor. We have recorded absorption spectra, thermal emission spectra, and laser-induced emission spectra of dense potassium vapor. These techniques all reveal a spectral feature near 1.1 μm which we believe originates in ³Σ⁺_g→³Σ⁺_u transitions of the K₂ molecule.     

The hydrogen compensated cation vacancy VOH− in magnesium oxide

H-doped MgO single crystals show a number of infrared absorption bands in the OH stretching region. H-doped, high purity, well-annealed MgO crystals (4N grade = 99.99%), grown from the melt, show a prominent group of four equally spaced bands at 3296, 3310, 3325 and 3341 cm^?1, while lower grade 3N MgO crystals exhibit only the first two bands and the third after X-irradiation. Until now these bands were assigned to different types of OH^? ions. The present spectra indicate that the four bands form a quadruplet which is assigned to the OH stretching fundamental of one proton substituting a divalent cation [OH^?V_Mg^″O^2?]^?. In this defect the proton is expected to behave as an off-center impurity, residing probably in an XY₈ multiple well potential in the [111] directions. The 8-fold degenerate ground level will split due to tunneling into A_2u, T_2g, T_1u, A_1g states, giving rise to the observed quadruplet. The quadruplet is expected, if the proton occupies the nearly spherical well of the tetrahedral sites above each face of the octahedron forming the XY₈ system. If the proton moves towards the trigonal sites in the (111) faces, the well becomes elliptical and the quadruplet will be reduced to a doublet.     

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.     

Physisorption of metal carbonyls on Cu(100)

Chromium hexacarbonyl (Cr(CO)₆) and cyclopentadienyl rhodium dicarbonyl ((η⁵ − C₅H₅)Rh(CO)₂) were physisorbed on the Cu(100) surface and their molecular orientations were deduced from their reflection-absorption infrared (RAIR) spectra. No thermal decomposition of the compounds was observed. Physisorbed Cr(CO)₆ exhibited a substantial degree of dipole-dipole coupling within the adlayer, which was successfully disrupted by coadsorption in Ar at 23 K. The large absorption coefficient of the T_1u mode and the different boundary conditions of this ultrathin layer on a surface resulted in the observation of the longitudinal optical mode, confirming that the molecule is oriented with one carbonyl group adjacent to the surface. A Lyndane-Sachs-Teller splitting of 75 cm⁻¹ was observed for the T^1u mode. The physisorbed layer of (η⁵ − C₅H₅)Rh(CO)₂ did not exhibit strong dipole-dipole coupling, and was oriented with the C₅H₅ (Cp) ring parallel to the surface.     

Laser absorption spectroscopy of the A1Σu+-X1Σg+(v′, v″) bands of Na2

Laser absorption spectra of the band system A¹Σ_u⁺-X¹Σ_g⁺(v′,v″) of Na₂ in the range between 16835 and 16960 cm^?1 are analyzed. The spectra are free of first-order-Doppler broadening at low internal temperature. Rotational and vibrational assignments of 10 bands are reported. Rotational and vibrational levels, especially the (22, 1) band, are found to be perturbed by the b³Π_u state. The band origins and line frequencies calculated from previously reported constants do not reproduce the observed values. The disagreement between the calculated and observed values is discussed. More accurate constants are needed to predict the line locations.     

Vibrational spectra of antiferromagnetic FeBO3

Transmission spectra of powdered ferric borate have been measured in the wave number region from 6000 cm^-1 to 30 cm^-1 at room and liq. N₂ temperatures. Eight absorption bands observed are assigned as three A_2u and five E_u phonon modes. Of those modes, the temperature dependence of the E_u mode ar 230 cm^-1 (300 K) and the A_2u mode at 277 cm^-1 (300 K) have been measured in the temperature range containing the Néel temperature. They do not show the influence of magnetic ordering.     

Infrared absorption in In-doped degenerate Hg1−xCdxTe

The infrared absorption spectra, including absorption edge spectra and below-gap absorption spectra, were investigated both experimentally and theoretically for an In-doped degenerate HgCdTe sample with an electron concentration N_e = 7.0 × 10¹⁷ cm^-3 for wavelengths 7 μm<L<17 μm at the temperatures 77 K <T< 300 K. The possibility of applying free-carrier absorption theory developed for InSb to HgCdTe is discussed. It is concluded that the virtual crystal approximation works fairly well for HgCdTe and that the two-mode Callen effective charge should be used in the calculation of free-carrier absorption coefficients to account for the two-mode character of the optical phonons of HgCdTe. Good agreement between theory and experiment in the below-gap absorption spectra was obtained. The concentration of ionized impurities was found to be N_imp=3.4 × 10¹⁸ cm^-3. A good account of the behaviour of absorption edge in the light of Burstein-Moss effect has also been given.     

Calculations of O2 absorption and fluorescence at elevated temperatures for a broadband argon—fluoride laser source at 193 nm

Calculations have been made of O₂ absorption and fluorescence in the Schumann-Runge B³Σ^-_u←X³Σ^-_g band system for excitation by a broadband argon fluoride excimer laser at 193 nm. Results are presented for line strengths, spectral absorption coefficients, relative fluorescence spectra, total fluorescence and integrated absorption coefficients. The calculations have been performed for 300, 500, 1000, 1500 and 2000 K, a range of temperatures typically found in combustion flows. The absorption coefficients and fluorescence yields found are large enough to encourage use of argon fluoride lasers for O₂ measurements in a variety of flows.     

Fluid synthesis and structure of a new polymorphic modification of boron nitride

A new previously unknown phase of boron nitride with a hardness of 0.41–0.63 GPa has been pre-pared by the supercritical fluid synthesis. The presence of a new phase is confirmed by the X-ray spectra and IR absorption spectra, where new reflections and bands are distinguished. The fundamental reflection of the X-ray diffraction pattern is d = 0.286–0.291 nm, and the characteristic band in the infrared absorption spectrum is observed at 704 cm^?1. The X-ray diffraction pattern and the experimental and theoretical infrared absorption spectra show that a new synthesized boron nitride phase can be a cluster crystal (space group 211) with a simple cubic lattice. Cage clusters of a fullerene-like morphology B₂₄N₂₄ with point symmetry O are arranged in lattice sites.     

Absorption of Ni-centres in alkali chlorides

Absorption spectra of Ni²⁺ doped NaCl, KCl, and RbCl were measured in the spectral range from 55,000 to 5,000 cm^?1. The bands in the UV region are ascribed to the transition 3t _1u(σ, π)→3e _g(σ) of NiCl₆ complex ion. The connection of the intensity of charge transfer andd-d transitions has been discussed.     

Optical investigation of HoFeO3

The absorption spectra of HoFeO₃ were investigated in the near infrared spectral region at temperatures of 1.2, 4.2, 20 and 77 °K respectively. At every temperatureT≦20 °K all the absorption lines show the same splitting which is attributed to the groundstate; this splitting is (7.2±0.5) cm^?1 at 20 °K and decreases to (4.9±0.8) cm^?1 extrapolated to 0 °K. From these splittings the holmium-iron and the holmiumholmium interactions can be deduced. Measurements with an external magnetic field yield a magnetic moment ofμ=(7.6±0.7)μ _B per holmium ion. The moments are directed at angles of ?28° and ?152° with respect to theb-axis.     

The 3ν1+ ν2Combination Band of HOCl: Assignments,Perturbations, and Line Intensities

The high-resolution spectra (0.012 cm⁻¹) of the 3ν₁+ ν₂combination band of hypochlorous acid HO³⁵⁽³⁷⁾Cl in the near infrared (∼11 478 cm⁻¹) have been measured using a titanium:sapphire intracavity laser absorption (ICLA) spectrometer. Line assignments, absolute intensities, and the total band intensity for both isotopomers are reported. In the course of the band analysis twoK_abranches (K_a= 2,3) were found to be perturbed via low-order Fermi-type (anharmonic) resonances by a dark perturber which has been identified to be the 2ν₁+ 2ν₂+ 3ν₃state. The data are compared with intensity predictions from simple empirical models and discussed with regard to detection limits for this molecule in the near infrared spectral region of the atmosphere.     

I.R. Lattice-vibration spectra of MnF2

The room temperature reflectivity of MnF₂ has been measured in the far i.r. between 50 and 800 cm^?1. The reflectivity spectra show four i.r.-active modes which can be identified as E_u and A_2u modes. The spectra also show structure which might be related to multiphonon effects. The dielectric functions were determined by fitting the reflectivity data with classical oscillator parameters.     

Judd-Ofelt analysis and near infrared emission properties of the Er ions in tellurite glasses containing WO3 and CdO

The influence of erbium (Er³⁺) ion concentration on the infrared emission at 1.5 μm in TeO₂-WO₃ and TeO₂-CdO-WO₃ glasses was studied. The samples were prepared by conventional melt quenching method. The optical properties were studied by measuring the absorption and luminescence spectra at room temperature. The Judd-Ofelt parameters (Ω_t), transition probabilities, branching ratios of various transitions and their radiative lifetimes were calculated from the optical absorption spectra. Absorption and emission cross-section spectra and the Stark Levels splitting for the ⁴I_13/2 to ⁴I_15/2 transition of Er³⁺ centered at 1.5 μm were determined.     

Absorption spectrum of C2 molecules near 1.06 μm

An intracavity laser spectrometer has been used to study the laser-spark absorption spectrum of C₂ radicals near 1.06 μm. The spectra recorded have been assigned, and the rotational lines of the transitions 3-0, 4-1, and 5-2 b ³Σ _g ^? -a ³Π _u and 2-1 and 1-0 A ¹Π _u -X ¹Σ _g ⁺ have been identified. The vibrational and rotational temperatures have been determined.