The infrared spectra of 12C32S, 12C34S, 13C32S,and 12C33S

Using a tunable diode laser spectrometer, the infrared absorption spectra of four isotopic species of carbon monosulfide have been observed in the positive column of a dc discharge of CS₂ and Ar. The wavenumbers of 115 vibration-rotation transitions between 1180.5 and 1266.1 cm^?1 have been measured. These lines were assigned to the 1-0, 2-1, 3-2, and 4-3 bands of ¹²C³²S, the 1-0 and 2-1 bands of ¹²C³⁴S and ¹³C³²S, and the 1-0 band of ¹²C³³S. These new data have been combined with the previous infrared and microwave results to determine Dunham coefficients (Y_ij), the Dunham potential expansion constants (a₀,a₁,a₂,a₃, and a₄), and the classical turning points by the RKR method.     

Infrared emission of 12C16O, 13C16O,and 12C18O

The combination of a new high-resolution grating spectrometer and a spontaneous emission source has made it possible to measure precisely the 1 → 0, 2 → 1, and 2 → 0 transitions of ¹²C¹⁶O relative to the accurately known ¹²C¹⁶O laser lines which have been referred to pure frequency standards by Eng et al. The 1 → 0 and 2 → 0 band centers agree to within 0.0002 cm^?1 with those measured relative to wavelength standards by Fourier transform spectroscopy (FTS). From a weighted simultaneous fit to the FTS-absorption, FTS-flame, our grating-emission, and microwave results, a set of calculated line positions was obtained for the 1 → 0, 2 → 1, and 2 → 0 transitions of ¹²C¹⁶O. The absolute accuracy of these line positions is believed to be ±0.0005 cm^?1 and we propose that the lines can be used as secondary wavenumber standards in the infrared.The spontaneous emission sequences v′ → (v′ ? 1) were measured for ¹²C¹⁶O up to v′ = 20, for ¹³C¹⁶O up to v′ = 11 (using a ¹³C-enriched sample), and for ¹²C¹⁸O up to v′ = 4 (in natural abundance). Internally consistent sets of Dunham coefficients were calculated from the best available data for the molecules of ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O.     

O2 broadening of carbon disulphide 12C32S2 in the v 3 and v 3—v 1 bands

Using a tunable diode laser spectrometer, we have measured O₂ broadening coefficients of ¹²C³²S₂ for 31 lines in the v ₃ fundamental band near 6.5 μm and 12 lines in the v ₃—v ₁ band near 11.4 μm. The collisional halfwidths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. The broadening coefficients of ¹²C³²S₂-O₂ are also calculated from semiclassical theory involving, in addition to electrostatic interactions, successively the atom-atom Lennard-Jones model and a simple formulation for the anisotropic dispersion forces, leading to more satisfactory results.     

High-resolution spectroscopy of the v2 = 2 a ← v2 = 1 s band of 15NH3

Twenty-four transitions of the v₂ = 2 a ← v₂ = 1 s hot band of ¹⁵NH₃ have been observed by an infrared microwave sideband laser spectrometer. In addition, 149 transitions of the band have been obtained by a Fourier transform spectrometer at a resolution of 0.02 cm⁻¹. A weighted least-squares analysis has been carried out and the rms deviation of the fit is 0.00097 cm⁻¹. It was necessary to include the Δ(K − l) = ±3 interaction between the v₂ = 2 a and the v₄ = a states in the analysis.     

Microwave spectra of carbonyl sulfide: Measurements of ground state and vibrationally excited 16O13C32S, 18O12C32S,and other isotopic species

Microwave measurements have been made on isotopically enriched samples of ¹³C-carbonyl sulfide and ¹⁸O-carbonyl sulfide. Centrifugal distortion constants and l-type doubling constants have been determined for these isotopically substituted molecules. Rotational constants have been measured for all vibrational states below 2150 cm^?1 and B_e values have been determined. The equilibrium bond distances calculated from different pairs of isotopes are compared and a substitution equilibrium structure is given. Some new measurements are also reported for the isotopic species ¹⁸O¹³C³²S, ¹⁸O¹³C³⁴S, ¹⁸O¹²C³⁴S, and ¹⁶O¹³C³⁴S.     

High-resolution spectroscopy of the v2 = 2 a ← v2 = 1 s band of 14NH3

Twenty-one transitions of the v₂ = 2 a ← v₂ = 1 s hot band of ¹⁴NH₃ have been observed by an infrared microwave sideband laser spectrometer with an absolute accuracy of 0.00002 cm⁻¹. One hundred and seventeen transitions of the band have been obtained by a Fourier transform infrared spectrometer at a resolution of 0.005 cm⁻¹. A weighted least-squares analysis of these data has been carried out to yield 17 molecular parameters for the v₂ = 2 a state. These parameters reproduce the experimental frequencies with a root mean square deviation of 0.000123 cm⁻¹. To calculate the frequencies to this accuracy it was necessary to take into account the Δ(K − l) = ±3 interaction between the v₂ = 2 a and v₄ = 1 a states.     

High-resolution infrared Fourier transform spectroscopy of SO in the X3Σ− and a1Δ electronic states

The v = 1 ← 0 vibration-rotation absorption bands of ³²S¹⁶O, ³⁴S¹⁶O, and ³²S¹⁸O in the ground electronic state, X³Σ⁻, and the v = 1 ← 0 vibration-rotation band of ³²S¹⁶O in the first excited electronic state, a¹Δ, were measured at 0.004 cm⁻¹ unapodized resolution with a high-resolution Fourier transform spectrometer coupled to a long path absorption cell. The v = 2 ← 0 vibration-rotation band of ³²S¹⁶O in the X³Σ⁻ state was also observed. Line positions for P- and R-branch transitions up to N = 44 for ³²S¹⁶O have been measured and analyzed yielding improved molecular parameters. The present measurements are compared with previous infrared and microwave measurements.     

High-resolution laser Stark and Fourier transform spectroscopy of DBr at 5.5 μm

A very close coincidence between the P(1) transition of the 1-0 band of D⁷⁹Br and a CO laser line has allowed the observation of a DBr laser Stark spectrum. The observed inverse Lamb dips resolve the Br hyperfine structure of the transition, and are used to determine the value of the dipole moment of DBr in the v = 1 state. A high-resolution Fourier transform spectrum of DBr in the region 1750 to 1900 cm^?1 has also been recorded and accurately measured. These new data, together with the best previous microwave and infrared measurements, are used to determine molecular parameters for DBr, and also result in improved secondary wavenumber standards for the 5.5-μm region.     

The perpendicular fundamental v5 of chloroform 12CH35Cl3: high resolution infrared study of the v5 band together with the millimetre-wave rotational spectrum

The infrared spectrum of the perpendicular fundamental v₅ of chloroform around 776 cm^?1 has been studied by applying two high resolution methods. A short range from the central part of the spectrum was measured with a diode laser by using a cold jet sample including chloroform in natural isotopic abundancies. More than 100 rotational lines of ¹²CH³⁵Cl₃ could be assigned. The whole band region was measured by a Fourier transform spectrometer at a resolution of 0.0010cm^?1. In this case an isotopically pure sample of ¹²CH³⁵Cl₃ was used. Starting from the results of the diode laser investigation more than 2000 lines could be assigned with J_max = 91 and K_max = 58. In addition to the infrared spectra, millimetre-wave lines also were measured. A total of 58 lines corresponding to J values 22, 23 and 35 at the excited vibration state v₅ = 1 were assigned and analysed. All the data from three different spectra were simultaneously fitted and, for example, the results v₀ = 775.961 50(3) cm^?1, 98, B₅-B₀ = ?0.180171(22) × 10^?3cm^?1, C₅ ? C₀ = ?0.170 57(15) × 10^?3cm^?1, and (Cζ)₅ = 0.047 5294(11) cm^?1 were obtained.     

Submillimeter microwave spectrum and spectroscopic constants of the OCS molecule: Isotopic species 16O12C33S and 18O12C32S

Microwave spectra of ¹⁶O¹²C³³S and ¹⁸O¹²C³²S in their natural isotopic abundances were investigated in the range 280–510 GHz. The effective rotational and centrifugal constants have been determined for all observed vibrational states. An analysis of the rotational spectrum taking account of l- and Fermi-resonances has been performed within each isotopic species.     

Infrared diode laser spectroscopy

Three types of lasers (double-heterostructure 66 K InAsSb/InAsSbP laser diode, room temperature, multi quantum wells with distributed feedback (MQW with DFB) (GaInAsSb/AlGaAsSb based) diode laser and vertical cavity surface emitting lasers (VCSELs) (GaSb based) have been characterized using Fourier transform emission spectroscopy and compared. The photoacoustic technique was employed to determine the detection limit of formaldehyde (less than 1 ppmV) for the strongest absorption line of the v₃ + v₅ band in the emission region of the GaInAsSb/AlGaAsSb diode laser. The detection limit (less than 10 ppbV) of formaldehyde was achieved in the 2820 cm⁻¹ spectral range in case of InAsSb/InAsSbP laser (fundamental bands of v₁, v₅). Laser sensitive detection (laser absorption together with high resolution Fourier transform infrared technique including direct laser linewidth measurement, infrared photoacoustic detection of neutral molecules (methane, form-aldehyde) is discussed.     

The infrared spectrum of 12C32S and 12C34S

The 2-0 vibration-rotation bands of ¹²C³²S and ¹²C³⁴S near 2530 cm^?1 have been measured with a high resolution spectrometer. The spectroscopic constants for these bands are given, as well as an improved set of Dunham coefficients for the X¹Σ⁺ state of ¹²C³²S.     

Absolute line wavenumbers in the near infrared: 12C2H2 and 12C16O2

40 absolute line wavenumbers in the 3v ₃ band of ¹²C¹⁶O₂ between 6927 cm^?1 and 6989 cm^?1 and 626 absolute line wavenumbers in the near infrared absorption spectrum of ¹²C₂H₂ between 7060 cm^?1 and 9900 cm^?1 have been measured using high resolution Fourier transform spectroscopy. The calibration of the CO₂ line wavenumbers relied on heterodyne frequencies available in the v ₁ + v ₃ band of ¹²C₂H₂ near 6556 cm^?1. The absolute uncertainty of the calibrated CO₂ line wavenumbers is estimated to 0.000 08 cm^?1. The acetylene spectra were calibrated using heterodyne frequencies available in the 2—0 band of ¹²C¹⁶O and the line wavenumbers obtained in the 3v ₃ band of ¹²C¹⁶O₂. The absolute uncertainty of the calibrated acetylene line wavenumbers is estimated to range from 0.0003 cm^?1 to 0.006 cm^?1 for strong to very weak isolated lines. Comparison with absolute line wavenumbers obtained independently at JPL in the 3v ₃ band of ¹²C₂H₂ near 9649 cm^?1, calibrated using absolute wavenumbers available in the 2—0 and 3—0 (near 6350 cm^?1) bands of ¹²C¹⁶O, shows very good agreement. Also, the vibration—rotation constants for the observed upper vibrational states of ¹²C₂H₂ were determined, but without accounting for the perturbations affecting these states.     

The 13C2 and 12C13C Ballik-Ramsay system

The infrared spectrum of the b³Σ⁻ → a³Π Ballik-Ramsay system has been observed for both ¹³C₂ and ¹²C¹³C isotopic species using high-resolution Fourier transform spectroscopy. Twelve bands: 0 → 0, 1 → 0, 1 → 1, 2 → 0, 2 → 1, 3 → 1, 3 → 2, 4 → 2, 4 → 3, 5 → 2, 5 → 3, 6 → 3 of ¹³C₂ and seven bands: 0 → 0, 1 → 0, 1 → 1, 2 → 0, 2 → 1, 3 → 1, 3 → 2 of ¹²C¹³C were identified in the spectral range 3500–12 000 cm⁻¹. Perturbations in the b³Σ⁻ (v = 0, 1, 2, 3) levels were reduced and accurate perturbation parameters derived from the analysis. A comparison with ab initio calculated spin-orbit coupling constants is presented.     

Diode laser measurements of line strengths and collisional half-widths in the ν1 band of OCS at 298 and 200K

Absolute line strengths and self-broadened half-widths have been measured at 298 and 200 K for spectral lines ranging from J = 1 to 55 in the ν₁ band (860 cm^-1) of ¹⁶O¹²C³²S, using a tunable diode laser spectrometer. The vibrational transition moment (6.412 ± 0.16 × 10^-2D) as well as the absolute intensity (29.63±1.48 cm^-2-atm^-1 at 298 K), of the ν₁ band are determined from these line-strenght measurements. By applying two semi-classical impact theories of collisional broadening, we have obtained results for half-widths at 298 and 200 K which are significantly larger than the experimental data for |m|<50. However, the variation of the linewidths with temperature is well reproduced theoretically.     

Laser Stark measurements on OCS including the observation of zero-field-forbidden ΔJ = 0, ±2 transitions

Laser Stark measurements have been made on the 02⁰000⁰0 and 03¹001¹0 vibrational transitions of ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, and ¹⁸O¹²C³²S, and on the 03¹001¹0 transition of ¹⁶O¹³C³²S, using a CO₂ laser. In addition to providing dipole moment information for excited vibrational states, these measurements give vibrational band centers accurate to several megahertz. To aid in optical pumping experiments, several near coincidences between CO₂ laser transitions and OCS absorption lines are discussed. Electric-field-allowed ΔJ = 0 transitions are observed for the 2ν₂ band of ¹⁶O¹²C³²S and ¹⁶O¹²C³⁴S, as well as ΔJ = 2 transitions for the same band of ¹⁸O¹²C³²S.     

Spectral measurements of high-temperature isotopic carbon dioxide in the 4.5- and 2.8-μm regions

High-resolution measurements have been made using the AFGL 2-m path difference Fourier transform spectrometer on isotopically enriched samples of carbon dioxide. Two regions were investigated: 2140–2320 and 3470–3770 cm⁻¹. The samples were observed in absorption at temperatures up to 800 K. Observed line positions to high rotational levels were obtained for 15 parallel bands with Δv₃ = 1 for the isotopic variants ¹³C¹⁶O₂, ¹³C¹⁶O¹⁸O, and ¹³C¹⁶O¹⁷O in the 4.5-μm region and for 23 bands of the type Δv₁ = 1, Δv₃ = 1 for the species ¹²C¹⁶O₂, ¹²C¹⁶O¹⁸O, and ¹²C¹⁸O₂ in the 2.8-μm region.     

Infrared spectrum of stannous oxide (SnO)

A tunable diode laser has been used to measure the infrared spectrum of stannous oxide (SnO) in the gas phase between 830 and 868 cm^?1. Measurements of the v = 1-0, 2-1, 3-2, and 4-3 transitions have been made at temperatures ranging from 930 to 1150°C. Over 175 infrared transitions of the nine most abundant SnO isotopic species have been combined with microwave measurements reported by others in a single least-squares analysis of the data to yield a set of eight Dunham coefficients for the X¹Σ⁺ state of SnO. The data have also been fit by a nonlinear least-squares procedure to obtain B_e, ω_e, and the first five Dunham potential constants. The band center for the vibrational transition of ¹²⁰Sn¹⁶O is found at ν₀ (v = 1?0) = 814.70249 ± 0.00027 cm^?1.     

Spectral intensities in the ν1 band of carbonyl sulfide and its isotopic species

A tunable diode laser was used to perform measurements of absolute lines intensities in the ν₁ fundamental of carbonyl sulfide. Spectra have also been recorded for the following isotopic species: ¹⁶O¹²C³⁴S, ¹⁶O¹³C³²S and ¹⁶O¹²C³³S. The vibrational band strength S_v⁰ was calculated at 298 K. The absolute intensity for 100% of ¹⁶O¹²C³²S species is found to be S_v⁰ = 29.69 ± 0.15 cm⁻² atm⁻¹ with the uncertainty covering three times the standard deviation. We have tried to determine the α-coefficient involved in the Hermann-Wallis factor F = (1 + αm + )² and the value is found to be negligible (−5 ± 8) × 10⁻⁵. The S_v⁰ value obtained for the other isotopic species is very close to the normal one.     

Dunham coefficients for seven isotopic species of CO

An extensive work on vibration-rotation spectra in the fundamental ¹Σ⁺ electronic state of CO is reported. More than 30 000 Doppler-limited measurements corresponding to about 8500 transitions of 255 bands of ¹²C¹⁶O, ¹²C¹⁸O, ¹³C¹⁶O, and ¹³C¹⁸O, most of them observed for the first time, have been obtained with a high information Fourier transform interferometer on the sequences Δv = 1, 2, and 3. The highest v and J values are 41 and 93, respectively. Experimental vibrational levels are then well observed up to three fourths of the dissociation energy limit. These accurate infrared wavenumbers, with an additional selected set of all previous measurements, have been simultaneously fitted to the Dunham expression in a weighted nonlinear least-squares calculation covering seven different isotopic species. It significantly improves both the number of parameters (U and Δ) obtained by the best previous work (35 instead of 23) and their corresponding standard deviations. The rms of the fit is equal to 13 × 10^?6 cm^?1 (390 KHz). Calculated wavenumbers from the 35 reduced Dunham and mass-scaling coefficients can then be used as secondary standards, even for transitions involving high v and J values of the various isotopic species. These new parameters should be a convenient and useful tool for several purposes, such as assignment of infrared laser lines and identification of microwave and infrared transitions in astronomical spectra. The Dunham coefficients Y are also reported for ¹²C¹⁶O, ¹²C¹⁷O, ¹²C¹⁸O, ¹³C¹⁶O, ¹³C¹⁷O, ¹³C¹⁸O, and ¹⁴C¹⁶O. These experimentally determined accurate Y should also be useful for further examination of the potential energy and dipole moment formulations.