Temperature dependence of pressure broadening of the N = 1− fine structure oxygen line at 118.75 GHz

The absorption profile of the N = 1− fine structure line of oxygen was recorded by a resonator spectrometer at a frequency range of 110-130 GHz at atmospheric pressure and different temperatures ranging from −21 °C up to +22 °C. Analysis of the observed line shape allowed determination of the temperature dependence of the line pressure broadening. The measured value of the temperature exponent is n = 0.74(5) for self-broadening. Consistency of the measurements is supported by simultaneous measurements of the line intensity, the line mixing parameter and the line center frequency, and by comparison of obtained values with previously known data.     

Reinvestigation of pressure broadening parameters at 60-GHz band and single 118.75 GHz oxygen lines at room temperature

Low pressure measurements of broadening parameters of the 118.75 GHz fine structure line of oxygen molecule have been made by a BWO-based spectrometer with acoustic detector (RAD) at room temperature. Pressure broadening parameters were obtained for the buffer gases O₂, N₂, Ne, He, Ar, H₂O, CO₂, and CO and have the following values 2.23 ± 0.01, 2.245 ± 0.02, 1.375 ± 0.02, 1.62 ± 0.03, 2.005 ± 0.02, 2.52 ± 0.04, 2.66 ± 0.08, and 2.31 ± 0.05 MHz/Torr, respectively. Measured central frequency is 118 750.340 ± 0.007 MHz. The central frequencies and broadenings by O₂ and N₂ of fine structure lines 1⁺, 5⁻, 7⁺, 11⁺, and 15⁻ belonging to the 60-GHz band are also measured. Comparison of previous and recent data on electronic, rotational, and fine structure lines broadenings reveals their close values (within 10%) and dependencies on corresponding rotational quantum numbers for these different oxygen spectra stretching from millimeter through submillimeter up to the optical bands. Such similarity could be used for estimation of the broadenings of not measured yet oxygen lines.     

Broadening, shifting, and line mixing in the 030 ← 010 parallel Q branch of N2O

The 03¹0 ← 01¹0 parallel Q branch of N₂O has been studied at 297 K and over the pressure range 1-130 torr. Absorption spectra were recorded using a high resolution (1.5 MHz or 5 × 10⁻⁵ cm⁻¹) and high signal-to-noise (>3500:1) mid-infrared spectrometer based on difference-frequency infrared generation in AgGaS₂. In the low-pressure range (1-11 torr) we obtained accurate values for the line strengths, the broadening coefficients, the weak mixing coefficients, and the overall shifting of the branch. The medium pressure results, ranging from 23 to 130 torr, were analyzed by treating the band as a whole, using a relaxation matrix formalism, based on an energy gap scaling law. We find, effectively, that only 36% of the rotationally inelastic collisions are associated with Q branch mixing, the rest presumably being associated with Q-P and Q-R mixing in the same vibrational band. The pressure shifting coefficient of the 03¹0 ← 01¹0 Q branch as a whole was also determined and found to be 5.8 × 10⁻³ cm⁻¹/atm towards lower frequencies.     

Spectral line parameters in the (4 ← 0) overtone band and the dipole moment function of HI

We present new measurements of the line strengths in the third vibrational overtone band in pure HI and its mixtures with Ne, Ar, and Xe, and report results of the Herman-Wallis analysis for this band. Significance of the higher-order terms in the polynomial representation of the dipole moment function is discussed. It is concluded that the spectroscopic data yield the dipole moment function fully described by a cubic polynomial in powers of the reduced displacement from the equilibrium bond length. In the Padé approximant for the dipole moment function, the vicinity of the saddle point near equilibrium also can be accurately fitted with a cubic polynomial. Pressure line broadening and shifting parameters are reported for mixtures of HI with rare gases.     

Spectral line parameters in the (3 ← 0) overtone band of the HI molecule and line-mixing in the band head

The linestrengths, self-pressure broadening and shifting coefficients have been measured for P₃ (10)- R₃ (12) lines in the second overtone band of hydrogen iodide. A dipole moment function in terms of the reduced nuclear displacement x = (R − R_e)/R_e is obtained using rotationless dipole matrix elements determined by the Herman-Wallis analysis of the (1, 2, 3 ← 0) HI bands: μ (x) = 0.4471(5) − 0.0770(2)x + 0.547(3)x² − 1.93(2)x³, in a full agreement with the function proposed previously [J. Mol. Spectrosc. 223 (2004) 67]. A close match is demonstrated of the results of most recent relativistic calculations [Phys. Chem. Chem. Phys. 6 (2004) 3779] with the spectroscopically derived electric dipole parameters for HI. Line-mixing in the band head is observed, the self-pressure shifting and broadening coefficients for the (3 ← 0) band lines are determined.     

Line mixing and speed dependence in CO2 at 6227.9 cm: Constrained multispectrum analysis of intensities and line shapes in the 30013 ← 00001 band

Line position, intensity and line shape parameters (Lorentz widths, pressure shifts, line mixing, speed dependence) are reported for transitions of the 30013 ← 00001 band of ¹⁶O¹²C¹⁶O (ν₀ = 6227.9 cm⁻¹). The results are determined from 26 high-resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath-Pierce Fourier transform spectrometer. To minimize the systematic errors of the retrieved parameters, we constrained the multispectrum nonlinear least squares retrieval technique to use quantum mechanical expressions for the rovibrational energies and intensities rather than retrieving the individual positions and intensities line by line. Self- and air-broadened Lorentz width and pressure-induced shift, speed dependence and line mixing (off-diagonal relaxation matrix elements) coefficients were adjusted individually. Errors were further reduced by simultaneously fitting the interfering absorptions from the weak 30012 ← 00001 band of ¹⁶O¹³C¹⁶O as well as the weak hot bands 31113 ← 01101, 32213 ← 02201, 40014 ← 10002 and 40013 ← 10001 of ¹⁶O¹²C¹⁶O in this spectral window. This study complements our previous work on line mixing and speed dependence in the 30012 ← 00001 band (ν₀ = 6347.8 cm⁻¹) [V.M. Devi, D.C. Benner, L.R. Brown, C.E. Miller, R.A. Toth, J. Mol. Spectrosc. 242 (2007) 90-117] and provides key data needed to improve atmospheric remote sensing of CO₂.     

Line shape parameters measurement and computations for self-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 bands, line mixing, and speed dependence

Transitions of pure carbon dioxide have been measured using a Fourier transform spectrometer in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra, recorded at a resolution of 0.008 cm⁻¹, were analyzed using the Voigt model and a Speed Dependent Voigt line shape model that includes a pressure dependent narrowing parameter. Intensities, self-induced pressure broadening, shifts, and weak line mixing coefficients are determined. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.     

Spectral line parameters in the (2 ← 0) overtone band and the dipole moment function of the HI molecule

We present here new high-resolution experimental data on the linestrengths and pressure-broadened Lorentzian widths for the P₂(13) to R₂(12) vibration-rotation lines in the first overtone absorption band of hydrogen iodide. By combining the measured linestrengths with our previous results for the fundamental band [J. Mol. Spectrosc. 218 (2003) 75] and with other published data for the higher-overtone bands of this molecule, an improved dipole moment expansion as a function of the dimensionless reduced nuclear displacement x is obtained: μ(x)=0.4471(5)−0.0772(2)x+0.542(3)x²−1.90(2)x³. This experimental dipole moment function is compared with the results of a few recent non-relativistic and relativistic ab initio calculations. The agreement between theoretical and experimental Herman-Wallis coefficients for the first two vibrational bands of HI is found best as ever reported before.     

Experimental investigation of the line center of Hg intercombination spectral line 253.7 nm perturbed by Kr

The collision broadening and shift of the Hg intercombination spectral line 253.7 nm (6¹S₀–6³P₁) perturbed by Kr has been investigated using a high-resolution scanning Fabry–Perot interferometer. The values of the pressure broadening and shift coefficients β and δ, respectively, for the studied line have been obtained. The obtained coefficients β and δ are compared with their corresponding published experimental values and also those calculated using Lindholm–Foley impact theory.     

Pressure broadening coefficients of the water vapor lines at 556.936 and 752.033 GHz

The air induced broadening coefficients of the pure rotational transitions of H₂O at 556.936 GHz (1₁₀←1₀₁), and 752.033 GHz (2₁₁←2₀₂) were measured by terahertz time-domain spectroscopy. The air broadening coefficient was determined to be for the 556.936 GHz line and for the 752.033 GHz line, respectively. The present broadening coefficients for the 556.936 GHz water line are significantly smaller than those of Markov and Krupnov [Measurements of the pressure shift of the 1(10)-1(01) water line at 556.936 GHz produced by mixtures of gases. J Mol Spect 1995:172;211-4] but relatively close to the values of the HITRAN database. The measured data may improve the accuracy of the abundance of water vapor retrieved from spectra obtained by the Odin/SMR satellite instrument. The effect on the satellite retrieval processing is discussed.     

Self-broadened CO line shapes in the v=2←0 band

Precise intensities, self-broadenings and shifts have been obtained for the ¹²C¹⁶O v=2←0 band from simultaneous fits of low-noise, high-resolution Fourier-transform spectra at pressures from 27 to 80 kPa (200-600 Torr). Observed line shapes exhibit deviations on the order of 1% from the conventional Voigt profile, primarily due to speed-dependent broadening and secondarily to line mixing. Dicke narrowing is reduced by over an order-of-magnitude from the diffusion value, presumably because of correlations between velocity- and phase-changing collisions.     

N2- and O2-broadening of CO2 for the (301)III ← (000) band at 6231 cm

The N₂- and O₂-broadening effect have been investigated for 10 absorption lines of the CO₂ (30⁰1)_III ← (00⁰0) band centered at 6231 cm⁻¹, in the range from P(28) to R(28) by a near-infrared diode-laser spectrometer. We have analyzed the observed line profiles with the Galatry function, and determined the N₂- and O₂-broadening coefficients precisely. The air-broadening coefficients for these lines have been derived. The present results are compared with those of the previous studies for this band and with some of the other bands.     

Theoretical study of oxygen adsorption at the Fe(1 1 0) and (1 0 0) surfaces

Electronic, magnetic and structural properties of atomic oxygen adsorbed in on-surface and subsurface sites at the two most densely packed iron surfaces are investigated using density functional theory combined with a thermodynamics formalism. Oxygen coverages varying from a quarter to two monolayers (MLs) are considered. At a 1/4 ML coverage, the most stable on-surface adsorption sites are the twofold long bridge sites on the (1 1 0), and the fourfold-hollow sites on the (1 0 0) surface. The presence of on-surface oxygen atoms enhances the magnetic moments of the atoms of the two topmost Fe layers. Detailed results on the surface magnetic properties, due to O incorporation, are presented as well. Subsurface adsorption is found unfavored. The most stable subsurface O, in tetrahedral positions at the (1 0 0) and octahedral ones at the (1 1 0) surface, are characterized by substantially lower binding than that in the on-surface sites. Subsurface oxygen increases the interplanar distance between the uppermost Fe layers. The preadsorbed oxygen overlayer enhances binding of subsurface O atoms, particularly for tetrahedral sites beneath the (1 1 0) surface.     

Structural properties of oxygen on InN(0 0 0 1) surface

First-principles calculations are performed to study the various structures of oxygen (O) adsorbed on InN(0 0 0 1) surfaces. It is found that the formation energy of O on InN(0 0 0 1) decreases with decreasing oxygen coverage. Of all the adsorbate induced surface structures examined, the structure of InN(0 0 0 1)-(2 × 2) as caused by O adsorption at the H₃ sites with 0.25 monolayers coverage is most energetically favorable. Meanwhile, nitrogen (N) vacancy can form spontaneously. Oxygen atoms may also substitute N atoms, or accumulate at the voids inside InN film or simply stay on the surface during growth. The oxygen impurity then acts as a potential source for the n-type conductivity of InN as well as the large energy band gap measured.     

N2-, H2-, and He-induced collisional broadening of the J = 24 ← 23 transition of HC3N located near 218.3 GHz at different temperatures

We report on experimental collisional relaxation of the J = 24 ← 23 line of HC₃¹⁴N, located near 218.3 GHz, induced by nitrogen, hydrogen, and helium. The measurements were carried out at selected temperatures in the 235-350 K range using a video-type spectrometer. The foreign gas broadening parameters and their temperature dependences were determined assuming Voigt lineshape profiles and the usual T⁻ⁿ temperature law. The experimental broadening parameters are compared with results derived using the ATC collisional formalism.     

Photoelectron spectroscopy study of oxygen adsorption on Mo2C(0 0 0 1)

Oxygen adsorption on the α-Mo₂C(0 0 0 1) surface has been investigated with X-ray photoelectron spectroscopy and valence photoelectron spectroscopy utilizing synchrotron radiation. It is found that oxygen adsorbs dissociatively at room temperature, and the adsorbed oxygen atoms interact with both Mo and C atoms to form an oxycarbide layer. As the O-adsorbed surface is heated at ≧800 K, the C-O bonds are broken and the adsorbed oxygen atoms are bound only to Mo atoms. Valence PES study shows that the oxygen adsorption induces a peculiar state around the Fermi level, which enhances the emission intensity at the Fermi edge in PES spectra.     

Water line parameters for weak lines in the range 9000-12 700 cm

A total of 7923 transitions previously derived from long pathlength, Fourier transform spectra of pure water vapor (Schermaul et al., J. Mol. Spectrosc. 211 (2002) 169) have been refitted and reanalyzed using a newly calculated variational linelist. Of these, 6600 lines are weaker than 1 × 10⁻²⁴ cm/molecule, for which reliable intensities are obtained. These weak lines include 1082 lines, largely due to H₂¹⁶O, which have not been previously observed. A total of 7156 lines were assigned resulting in 329 new energy levels for H₂¹⁶O spread over 32 vibrational levels. Estimates are also given for the band origins of the (022), (140), and (051) vibrational states.     

Line mixing effects in the ν2 + ν3 band of methane

This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν₂ + ν₃ band of ¹²CH₄. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν₂ + ν₃ transitions between 4410 and 4629 cm⁻¹ are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm⁻¹ atm⁻¹ at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm⁻¹ atm⁻¹ at 296 K.     

A bidirectional 60 GHz RoF system based on FWM in a semiconductor optical amplifier

In this study, a bidirectional 60 GHz RoF systems based on four-wave mixing (FWM) in semiconductor optical amplifier (SOA) is proposed. Two key techniques are included in such a scheme, namely, generation of 60 GHz modulating signals and distribution of 60 GHz local oscillator. The analytical model is theoretically analyzed and then confirmed by numerical simulations. Results of this study demonstrate that such a scheme can offer realistic solutions to support future mobile broad-band applications.     

Water vapour line assignments in the 9250-26 000 cm frequency range

Line parameters for water vapour in natural abundance have recently been determined for the 9250-13 000 cm⁻¹ region [M.-F. Mérienne, A. Jenouvrier, C. Hermans, A.C. Vandaele, M. Carleer, C. Clerbaux, P.-F. Coheur, R. Colin, S. Fally, M. Bach, J. Quant. Spectrosc. Radiat. Transfer 82 (2003) 99] and the 13 000-26 000 cm⁻¹ region [P.-F. Coheur, S. Fally, M. Carleer, C. Clerbaux, R. Colin, A. Jenouvrier, M.-F. Mérienne, C. Hermans, A.C. Vandaele, J. Quant. Spectrosc. Radiat. Transfer 74 (2002) 493] using a high-resolution Fourier-transform spectrometer with a long-path absorption cell. These spectra are analysed using several techniques including variational line lists and assignments made. In total, over 15 000 lines were assigned to transitions involving more than 150 exited vibrational states of H₂¹⁶O. Twelve new vibrational band origins are determined and estimates for a further 16 are presented.