Infrared bands of the HCNO molecule

Several vibration rotation bands of the H¹²C¹⁴N¹⁶O molecule have been studied by using high resolution vacuum grating infrared spectrographs. A linear molecular model has been used in establishing the vibrational assignments and evaluating the molecular constants. A value of 224.101 cm^?1 has been determined for the band center of the ν₅ fundamental by application of the Ritz combination principle. Future efforts will be directed to arriving at a similar result for the ν₄ fundamental.     

The rotational spectrum of HCNO in excited bending combination states

Millimeter wave rotational transitions of HCNO have been measured and assigned for 25 different sublevels in the vibrational states v₁v₂v₃v₄v₅ = 00004, 00012, 00013, 00021, 00022, and 00101. The measurements extend to 252 GHz covering J values up to J = 11 ← 10. Accurate effective constants B_eff and D_eff were obtained for all of these levels. Each state was treated separately, because of the quasilinearity of the ν₅ mode, and the lines were analyzed in terms of an effective Hamiltonian for linear molecules. Several Coriolis-type resonances between levels with adjacent l values were found. One set of resonances, analogous to that found earlier for lower levels, could be analyzed. Fits to the effective Hamiltonian were unsatisfactory in reproducing some of the measured frequencies, indicating resonances which were not analyzed, but the constants obtained show the trend in the parameters of the effective Hamiltonian as a function of bending excitation.     

Pure rotational spectrum of carbonyl sulfide in the far-infrared

The pure rotational spectrum of OCS has been studied by Fourier transform at room temperature over the frequency range 20–42cm⁻¹. The ground state rotational lines were observed for OC³²S up to J = 103. It has been possible also to identify the rotational lines for OC³⁴S in the ground state and for OC³²S in the ν₁ = 1 level.     

Identification of HBr isotopes in the far-infrared stratospheric spectrum

A detailed analysis is reported of high resolution IR theoretical spectra. Identification of spectral lines of HBr isotopes is made for observation conditions in the stratosphere (versus altitude, zenithal angle and concentration). The calculation of spectra suggests that a concentration of HBr higher than 6 pptv is required to detect some spectral lines of this constituent in experimental spectra.     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.     

Cusp satellite bands in the spectrum of molecule

We report measurements and a theoretical explanation of the cusp-shaped satellite bands in the blue wing of the cesium D₂ resonance line which have been observed for the first time. The bands are identified as transitions where the upper state dissociates into the 6 ²P _3/2 + 6 ² S _1/2 atomic asymptote. The experiment has been performed using a standard absorption setup, computer controlled data acquisition and computer data processing. We have shown that the peculiar shape of the difference-potential curve is solely responsible for the spectrum containing the cusp-shaped satellite bands. The appearance of these satellite bands has been discussed and explained relating the theory of satellite bands to the catastrophe theory. The shape of the line wing and of the satellite bands have been calculated using the Fourier transform technique. To ensure a more stringent comparison between the experimental and the theoretical spectrum, we have analyzed and compared the derivatives of the measured and the calculated satellite band shape. On the contrary to the customary direct comparison between the measured and the calculated absorption coefficient, the derivative clearly shows all differences and resemblances between satellite band profiles. The degree of coincidence of the experimentally observed and the theoretically calculated satellite band shape can be used as an ultimate check on the assessment of the quality of potential-energy curves involved in the formation of satellite bands. Received: 1 October 1997 / Revised: 14 January 1998 / Accepted: 24 February 1998     

The far-infrared absorption spectrum of electron-hole drops in silicon

We report on the first observation of the absorption spectrum of electron-hole drops in silicon. The absorption at 14°K consists of a broad peak at 34.2 ± 0.2 meV in the far-infrared spectral range. The lineshape can be well fit with a model that uses Mie theory of light absorption by small particles. The model includes both intra and interband terms. We find a plasma frequency of 51.9 ± 0.4 meV and from this we calculate a electron-hole density in the drops of (3.37 ± 0.06) × 10¹⁸ cm^?3.     

Temperature dependence of the far-infrared absorption spectrum of gaseous methane

The rototranslational absorption spectrum of gaseous methane has been measured at seven different temperatures from 296 to 140 K. We have analyzed both the spectral moments and the experimental absorption shapes, assuming that only octupolar and hexadecapolar induction mechanisms contribute to the absorption. This assumption allows us to parameterize the temperature dependence of both the intensity and the shape of the absorption band. The results obtained indicate that other contributions to absorption are not negligible.     

Bolometric measurement of the far-infrared absorption spectrum of single-crystal tetrathiafulvalene-tetracyanoquinodimethane

The far-infrared absorption spectrum of single-crystal TTF-TCNQ has been measured with high resolution by using the crystal as a bolometric detector at 7 K. The spectrum contains weak lattice modes, stronger intra-molecular modes with splittings due possibly to electron-phonon interactions, a direct gap near 300 cm^?1, a possible indirect gap near 100 cm^?1, and a possible pinned Fröhlich mode at low energy.     

Calculation of the far-infrared spectrum of a water-vapor molecular laser

The theory of partial population inversion between vibrational-rotational states in molecular media is applied for a molecular laser using vapors of H₂O as active media. Two conditions of laser action in such media are discussed — population inversion and gain. The lines in the far-infrared at which such a laser can generate are predicted and the relative intensities of these lines, are calculated.The paper was mainly prepared during the author's stay at the University of Western Ontario, London (Ontario), Canada.     

The high-resolution far-infrared spectrum of methane at the SOLEIL synchrotron

As a tetrahedral molecule, methane has no permanent dipole moment. Its spectrum, however, displays faint absorption lines in the THz region, due to centrifugal distorsion effects. This is important for planetary applications since this region is used to measure methane concentration in some planetary atmospheres, in particular on Titan. Up to now, all measurements relied either on some old low resolution infrared absorption spectra, or on high resolution Stark measurements for low J values only. Even if these results have been reexamined recently [Wishnow EH, Orton GS, Ozier I, Gush HP. The distorsion dipole rotational spectrum of CH₄: a low temperature far-infrared study. J Quant Spectrosc Radiat Transfer 2007;103:102-17], it seemed highly desirable to obtain much more precise laboratory data.The high-intensity synchrotron radiation, combined with a 151.75±0.1 m optical path in a White cell and a Bruker IFS 125 HR FTIR spectrometer at the AILES beamline of SOLEIL, enabled us to record this very weak spectrum at high resolution for the first time. Spectra were obtained in the 50-500 cm⁻¹ wavenumber range at 296 K and 9.91, 20, 50 and 100 mbar with a resolution of 0.00074, 0.00134, 0.0034 and 0.0067 cm⁻¹ (FWHM of the sinc function), respectively. The rotational clusters are fully resolved and the good signal-to-noise ratio has enabled precise measurements of transition intensities (92 cold band lines and 96 Dyad-Dyad hot band lines, with normal abundance intensities in the range 2×10⁻²⁶-1×10⁻²⁴ cm⁻¹/(mol cm⁻²)), yielding an accurate determination of the dipole moment derivatives. Such results should allow a better determination of CH₄ concentration in planetary objects.     

The far-infrared laser magnetic resonance spectrum of the CH radical

Transitions between the spin-rotational levels of the ¹³CH radical in the v=0 level of the ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. These measurements have been combined with the previous measurements of the lambda-doubling intervals of the molecule [J. Chem. Phys. 85 (1986) 1276 ] to determine an improved set of molecular parameters for ¹³CH. The analysis provides accurate predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field. A comparison is made with the values of the corresponding parameters of ¹²CH which reveals small effects due to the breakdown of the Born-Oppenheimer approximation.     

Role of interactions in the far-infrared spectrum of a lateral quantum-dot molecule

We study the effects of electron-electron correlations and confinement potential on the far-infrared spectrum of a lateral two-electron quantum-dot molecule by exact diagonalization. The calculated spectra directly reflect the lowered symmetry of the external confinement potential. Surprisingly, we find interactions to drive the spectrum towards that of a high-symmetry parabolic quantum-dot. We conclude that far-infrared spectroscopy is suitable for probing effective confinement of the electrons in a quantum-dot system, even if interaction effects cannot be resolved in a direct fashion.     

The far-infrared spectrum of fluoroform (CHF3)

The far-infrared spectrum of fluoroform has been recorded in the region between 7 and 60 cm⁻¹ at a resolution of 0.002 cm⁻¹. More than 1400 rotational transitions in the ground state have been measured and assigned up to J″ = 80. Simultaneous analyses of these measurements and of microwave and millimeter-wave data reported previously have been performed. Improved values of the ground state rotational and centrifugal distortion constants, including the sextic distortion constants reported for the first time, have been obtained. Rotational transitions in a few low-lying vibrational states have also been observed.     

Signature of symmetry of laterally coupled quantum dots in far-infrared spectrum

We study the effect of structure asymmetry on the energy spectrum and the far-infrared spectrum (FIR) of a lateral coupled quantum dot. The calculated spectrum shows that the parity break of coupled quantum dot results in more coherent superpositions in the low-lying states and exhibits unique anti-crossing in the two-electron FIR spectrum modulated by a magnetic field. We also find that the Coulomb correlation effect can make the FIR spectrum of coupled quantum dot without strict parity deviate greatly from Kohn theorem, which is just contrary to the symmetric case. Our results therefore suggest that FIR spectrum may be used to determine the symmetry of coupled quantum dot and to evaluate the degree of Coulomb interaction.     

Detection of atomic oxygen and further line assignments in the far-infrared stratospheric spectrum

The analysis of the high resolution far infrared emission spectrum of the stratosphere has made possible the identification of two features due to atomic oxygen. Several other new features have been assigned on the basis of updated line compilations. The possible detection of HBr, HO₂ and H₂O₂ in the far infrared is discussed.     

Part of the far-infrared laser magnetic resonance spectrum of the HF free radical

Transitions between the spin-rotational levels of the HF⁺ radical in the v=0 level of the X²Π ground state have been observed by the technique of laser magnetic resonance at far-infrared wavelengths. Because of the large spin-orbit coupling in this ²Π state, the detection of the fine-structure transitions required the use of very short-wavelength laser lines (down to 40 μm). These observations have provided accurate information on the ¹⁹F hyperfine splittings in rotational levels of the upper spin component for the first time which has enabled the complete determination of the hyperfine structure for this molecule. An effective Hamiltonian was used to model the experimental measurements; this provided considerably more accurate values for the various molecular parameters than previously available. Using these parameters, predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field have been made.