Diode-laser measurements of oxygen-broadened linewidths in the ν1 band of OCS

Pressure-broadening parameters of 25 lines belonging to the ν₁ band of ¹⁶O¹²C³²S in collision with O₂ have been measured with a tunable diode-laser spectrometer. From these coefficients and previously measured N₂-broadening coefficients, smoothed values of air-broadening parameters of OCS have been derived. The experimental results for O₂ broadening are compared with values calculated on the basis of the Anderson-Tsao-Curnutte theory and an improved semiclassical impact theory in which we used a simple formalism for the nonelectrostatic anisotropic potential. The latter theory, which has also been applied by considering an atom-atom interaction model, yields results in overall agreement with experimental data.     

Diode laser measurements of line strengths and widths in the 4.5-μm bands of N2O

We have made line-strength measurements in the N₂O ν₃-fundamental region using a tunable diode-laser spectrometer. From these measurements and the Herman-Wallis factor determined by Boissy et al., we find the ν₃-fundamental band strength to be S_v = 1203 ± 22 cm⁻² atm⁻¹ at 297 K. Line-broadening parameters for two ν₃-fundamental lines were determined using nitrogen (N₂) as the broadening gas. Measured strengths and N₂ line-broadening parameters for several (ν¹₂ + ν₃ − ν¹₂) hot-band lines are also presented.     

Diode laser spectroscopy of the ν1-ν3 band of CF335Cl at 15.84 μm

The vibration-rotation spectrum of CF₃Cl, with natural isotopic abundance, has been recorded in the 622- to 641-cm⁻¹ region using a tunable diode laser spectrometer. The K structure of many P(J) and R(J) manifolds of the ν₁-ν₃ difference band of CF₃³⁵Cl has been resolved and positively identified. The rotational analysis has been extended in the P and R branches up to J = 39 and 47, respectively, and more than 650 lines have been assigned. A least-squares fit of the observed transitions to the energy expression including the quartic centrifugal distortion terms was performed and molecular constants for the ν₁-ν₃ difference band were determined. From the obtained parameters the ν₃ band center of CF₃³⁵Cl was evaluated as 476.9750(4) cm⁻¹ and the values of α₃^A and α₃^B were derived to be 50(1) × 10⁻⁶ and 82.9(6) × 10⁻⁶ cm⁻¹, respectively.     

Diode laser spectroscopy of the ν1 and ν3 bands of thiazyl fluoride (FSN)

The ν₁ (FS stretch) and ν₃ (SN stretch) bands of FSN have been measured with Dopplerlimited resolution using a diode laser spectrometer. An accurate set of band constants were determined for ν₁ from a simultaneous fit to 265 infrared data and 73 ground state rotational transitions. The ν₃ band was found to be perturbed as the result of a Coriolis-type interaction between the states (0, 0, 1) and (1, 2, 0). Further difficulties with ν₃ were produced by the presence of many strong absorption lines from an SO₂ impurity. A limited set of effective band constants were determined for this band. Some general aspects of Q-branch absorption line patterns are briefly discussed.     

Diode laser spectroscopy of the ν4 (HCN bend) band of HCNH+

The ν₄ (HCN bend) band of the HCNH⁺ ion has been observed by diode laser spectroscopy using a magnetic field modulation technique. Twenty-three Q-, P-, and R-branch lines were observed and analyzed to yield the rotational, centrifugal distortion, and l-type doubling constants for the ν₄ state. The band origin was determined to be 801.5934(6) cm⁻¹.     

Measurements of the line strengths,N2− and O2-broadened half-widths in the ν3, ν1+2ν2 and 2ν1 bands of 14N2 16O at room temperature

The line strengths, N₂? and O₂-broadened half-widths in the ν₃, ν₁+2ν₂ and 2ν₁ bands of ¹⁴N₂ ¹⁶O were determined from spectra obtained by a high-resolution Fourier transform spectrometer at room temperature. The squared vibrational transition dipole moments and the coefficients of the Herman–Wallis factor were also determined for these bands. The squared vibrational transition dipole moments for these bands agreed with the values of HITRAN and high-resolution experiments within 6%. The N₂? and O₂-broadened half-widths were in agreement with the results of recent high-resolution experiments. The air-broadened half-widths were calculated using the smoothed N₂? and O₂-broadened half-widths and compared with the compiled values in the HITRAN database.     

Diode laser measurement of line strengths and air-broadening coefficients of CO2 and CO in the 1.57 μm region for combustion diagnostics

Spectral measurements of two line pairs of CO₂ and CO in the temperature range 300–1000 K at 1.573 µm were performed using a fiber-coupled distributed feedback (DFB) diode laser. The two line pairs can be used in a tunable diode laser (TDL) absorption sensor for simultaneously detecting CO₂ and CO gas in a single scan of the diode laser. The spectral parameters (line strengths, air-broadening coefficients and the temperature exponent n) of the two pairs are presented. The measured data agree well with existing databases (HITRAN 2004 and HITRAN 2008), the discrepancies being less than 5% for most of the probed transitions. Although the HITRAN database is a useful tool for sensor design, we found that laboratory measurements of the spectroscopic data for the line pair selected for high-temperature sensors are necessary for establishing the uncertainty for accurate measurements.     

Diode laser measurements of air and nitrogen broadening in the ν2 bands of HDO,H216O,and H218O

Pressure-broadening coefficients for several rotation-vibration lines in the ν₂ bands of HDO, H₂¹⁶O, and H₂¹⁸O have been determined from laboratory spectra recorded in the 1260- to 1360-cm⁻¹ region with a tunable diode laser spectrometer system. Air and nitrogen were used as the broadening gases and, for all the measured transitions, the nitrogen-broadened half-widths were found to be consistently larger than the corresponding air-broadened half-widths by about 12%. The results have been compared to previously published values when appropriate.     

Tunable diode laser measurements of absolute linestrengths in the HNO3 ν2 band near 5.8 μm

Absolute linestrengths of selected lines in the υ₂ band of HNO₃ have been measured using a tunable diode laser spectrometer operating in a sweep integration mode. The direct measurement technique has been employed to obtain line intensities at 296 K for 22 isolated lines in the 1720–1725 cm^-1 region. The reported linestrengths have estimated uncertainties of 4%, a significant portion of this uncertainty arising from spectral interference from hot band transitions. From these linestrength measurements, an integrated band intensity of 1375 cm^-2-atm^-1 at 296 K is inferred.     

High-resolution spectrum of the ν9 band and reinvestigation of the ν8 band of cis-CH3ONO

The infrared spectrum of methyl nitrite CH₃ONO has been recorded at a spectral resolution of 0.003 cm^?1 using a Fourier-transform spectrometer Bruker IFS125HR. The ν₈ band of the cis isomer has been reinvestigated in the 780–880 cm^?1 spectral range to complete the study made by Goss et al. (2004) [3] and to fit the internal rotor splittings. The BELGI-IR program, which enables us to treat an isolated infrared band for asymmetric molecules containing one internal methyl rotor has been used for the analysis and predictions of spectra. Finally 1036 lines (913 A-type and 123 E-type lines for J≤50 and K_a≤28) have been assigned for the cis isomer and fitted with a standard deviation of 0.00047 cm^?1.Furthermore, for the first time, the ν₉ band of cis-CH₃ONO was investigated in the 540–660 cm^?1 spectral range and rather large internal rotation splittings were also observed at higher J values. For the ν₉ band, the effective approach performed with the BELGI-IR program allowed us to analyze and reproduce 682 lines up to J=50 and K_a=18 with a standard deviation of 0.00051 cm^?1. The multiple vibration–rotation–torsion interactions, which are likely to occur between the excited v₉=1 and v₈=1 states and the torsional manifolds are discussed.     

Stark modulation infrared diode laser spectroscopy of the ν6 + ν8 band of diacetylene

The infrared diode laser spectrum of the ν₆ + ν₈ band of diacetylene (HCCCCH), i.e., a combination band of symmetric π_g (ν₆) and antisymmetric π_u (ν₈) CCH bending vibrations, was recorded by the Stark and source modulation techniques. The analysis of the Stark modulation spectrum allowed us to locate the 2ν₆ (Σ_g⁺) and 2ν₈ (Σ_g⁺) vibrational states, which are inaccessible by infrared transitions from the ground state. It is also shown that the Stark modulation spectrum can be used to confirm the rotational assignment of the ν₆ + ν₈ band.     

Line broadening,shifting and mixing parameters for the ν1 + ν3 band of OCS perturbed by N2 and O2

In this paper, we report measured Rosenkranz N₂- and O₂-broadening, induced pressure-shift and mixing coefficients for OCS in the ν₁ + ν₃ band, using a multi-pressure fitting technique applied to the measured shapes of the lines, including the interference effects caused by the line overlaps. These measurements were made by analysing six laboratory absorption spectra recorded at 0.004 cm^?1 resolution using the Fourier transform spectrometer Bruker IFS125HR located at the Laboratoire Interuniversitaire des Systèmes Atmosphériques, in Créteil. The spectra have been recorded in the 1850–3000 cm^?1 wave number range at 295 K, using a multipass absorption cell with an optical path of 3.249 m. The total sample pressures ranged from 5.97 to 83.28 Torr with OCS volume mixing ratios between 0.001 and 0.013 in nitrogen or oxygen. We have been able to determine the N₂- and O₂-pressure-broadening coefficients of 81 ν₁ + ν₃ transitions with rotational quantum number J up to 50. The measured N₂- and O₂-broadening coefficients range from 0.0815 ± 0.0698 to 0.1169 ± 0.1027 cm^?1 atm^?1 at 295 K, respectively. Most of the measured pressure shifts are positive. The reported N₂- and O₂-induced pressure-shift coefficients vary from about ?0.0103 ± 0.0092 to 0.0097 ± 0.0092 cm^?1 atm^?1, respectively. We have examined the dependence of the measured broadening parameters on the quantum number m (m = ?J for the P branch and m = J + 1 for the R branch) and also developed an empirical expression to describe the broadening coefficients in terms of |m|. On average, this empirical expression reproduces the measured broadening coefficients to within 2%. Using a semi-classical Robert and Bonamy formalism, the theoretical broadening coefficients have been calculated at room temperature and compared with the experimental results. The theoretical results of the broadening coefficients are in very good overall agreement with the experimental data (2%).     

The equilibrium structure of disulfur monoxide: Diode laser spectroscopy of ν1 and ν3 of S218O and ν3 of S216O

Diode laser spectroscopy of ν₁ and ν₃ of ³²S₂¹⁸O and ν₃ of ³²S₂¹⁶O has been carried out and several hundred transition frequencies were measured with a nominal accuracy of ±0.001 cm⁻¹. These data have been combined with earlier microwave and diode laser measurements to produce accurate rotational and distortion constants for the (0, 0, 0), (1, 0, 0), and (0, 0, 1) vibrational states of both isotopic species. These results were combined with microwave data from (0, 1, 0) of both isotopes to allow and equilibrium structure for S₂O to be calculated.     

Broadening and collisional interference of lines in the IR spectra of ammonia: Self-broadening in the ν<Subscript>1</Subscript> band

The relaxation parameters of the lines of the P, Q, and R branches of the ν₁ ammonia ν₁ band are calculated in the case of self-broadening. In the case of doublets, the effects of collisional interference of the doublet components have been taken into account. It is shown that the cross-relaxation parameters of the components can reach ~60% of the values of the self-broadening coefficients, which gives rise to the narrowing of the components and indicates that the isolated line approximation is inapplicable. Comparison with experimental data is made. Good agreement for self-broadening coefficients is obtained. In the case of the self-shift coefficients, discrepancies are considerable in both magnitude and sign, and it is impossible to elucidate their reasons without invoking additional experimental data.     

Absolute line intensities and self-broadening coefficients in the ν3 − ν1 band of carbon dioxide

Using a tunable diode-laser spectrometer, we have measured the self-broadening coefficients and strengths of 26 absorption lines in the ν₃ ? ν₁ band of ¹²CO₂ and ¹³CO₂ at room temperature. These lines, ranging from P(34) to R(40), are located around 960.9 and 913.4 cm^?1, respectively for the ¹²CO₂ and ¹³CO₂ molecules. The collisional widths and the intensities were obtained by fitting Voigt and Rautian and Sobel’man profiles to the measured shapes of the lines. From the individual line intensities and using a least-squares method, we have determined the vibrational band strength as well as the Herman–Wallis factors for the ν₃ ? ν₁ band of ¹²CO₂ and ¹³CO₂.     

Diode laser spectroscopic measurement of line shape of (ν1+3ν3) band transitions of acetylene

A near-infrared diode laser spectrometer is set up to study the absorption line shape of acetylene in the 782 nm region. The second-derivative spectra recorded by source modulation technique have enhanced sensitivity. Careful choice of operating current and diode temperature leads to distortion-free line shape for six rotational components of the (ν₁+3ν₃) overtone-combination mode of acetylene. Self- and nitrogen-broadening coefficients and line-strength parameters have been extracted by fitting the observed line shape with Voigt profiles. There is no evidence of the effect of velocity changing collisions on the line shape in this near-infrared band. Received: 6 July 1998 / Revised version: 2 November 1998 / Published online: 10 March 1999     

Measurements and calculations of ethylene line-broadening by argon in the ν7 band at room temperature

Argon broadening coefficients are measured for 32 vibrotational lines in the ν₇ band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3 ≤ J ≤ 19, 0 ≤ K_a ≤ 4, 2 ≤ K_c ≤ 19 in the P, Q and R branches are located in the spectral range 919–1023 cm^?1. The fitting of experimental line shapes with Rautian profile provides collisional widths slightly larger than those derived from the Voigt profile. The independent theoretical estimation of these line widths is performed by the semiclassical approach of Robert-and-Bonamy type with exact isotropic trajectories generalized to asymmetric tops. Even with a rough atom–atom intermolecular potential model the calculated values show good agreement with experimental results.     

Absolute line intensities in the ν1 + 3ν3 band of 12C2H2 by laser photoacoustic spectroscopy and Fourier transform spectroscopy

Line intensities and self-broadening coefficients in the ν₁ + 3ν₃ band of ¹²C₂H₂ near 0.8 μm at room temperature were measured by means of both laser photoacoustic and Fourier transform spectroscopy. An experimental protocol has been developed to obtain absolute intensities from the photoacoustic measurements. Namely, the spectrometer was calibrated using water vapour line intensities available in Hitran 1996 [L. S. Rothman et al. (1998) J. quant. Spectrosc. Radiat. Transfer, 60, 665–710]. These photoacoustic line intensities were found to be on average 5% higher than corresponding measurements performed using Fourier transform spectroscopy, the accuracy of the latter being estimated to better than 4%. The accuracy of the photoacoustic intensities is discussed. Previous results from the literature [F. Herregodts, D. Hurtmans, J. Vander Auwera, and M. Herman (1999) J. chem. Phys., 111, 7954—7960] are revised.