RESUMEN

We studied the R(0) line profile in the CH4 v4 band from room temperature to 188 K with N2 as a perturber, to 100 K with O2 as perturber, and from room temperature to 15 K using He as a perturber. The N2 and O2 measurements were performed over a total pressure range of 15-110 mbar, and for the He measurements the maximum sample pressure at 15 K was 1.10 mbar. Broadening parameters were determined, taking into account the confinement narrowing (Dicke effect), and narrowing parameters, deduced from the soft or hard collision model, are compared with the dynamic friction coefficient calculated values. We also obtained preliminary values for the temperature dependence of the N2, O2 and He line broadening parameters for this transition.

Asunto(s)

Frío , Metano/análisis , Espectrofotometría/métodos , Helio/química , Nitrógeno/química , Oxígeno/química , Presión , Espectrofotometría/instrumentación

RESUMEN

Two Q branches of C(2)H(2) near 716.3 and 719.9 cm(-1) belonging to the (nu(4) + nu(5))(0) - nu(1f)(4) and 2nu(0)(5)-nu(1f)(5) bands, of Sigma <-- Pi symmetry, have been studied for He and N(2) perturbers at pressures ranging from 0.05 to 1 atm, using a tunable diode-laser spectrometer. To interpret the line-mixing effects observed in these spectra, we have applied a model based on the energy-corrected sudden approximation whose parameters have been only derived from line-broadening data. This model provides satisfactory agreement with experimental bandshapes for both bands and perturbers, especially at pressures higher than 0.1 atm. The Q-branch profiles for C(2)H(2)-He are higher and narrower than those obtained for C(2)H(2)-N(2) at the same pressure as the result of smaller broadening coefficients and larger line-mixing effects in the former system. Copyright 2000 Academic Press.

RESUMEN

N(2)-broadening coefficients have been measured for 30 lines of cyanogen chloride ((35)Cl(12)C(14)N) at room temperature in the P and R branches of the nu(1) band, using a tunable diode-laser spectrometer. These lines, with J values ranging from 0 to 55, are located in the spectral range 694-736 cm(-1). The collisional widths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. The broadenings coefficients of (35)ClCN-N(2) have also been calculated from a semiclassical theory involving the atom-atom Lennard-Jones model for the intermolecular potential in addition to electrostatic interaction. Copyright 2000 Academic Press.

RESUMEN

N(2)-broadening coefficients have been measured for 35 lines of C(2)H(4) in the nu(7) fundamental transition, using a tunable diode-laser spectrometer. These lines with 3

RESUMEN

Absolute line intensities were measured at high resolution with a tunable diode laser. This work concerns the 2nu(0)(2) band of cyanogen chloride ClCN in the region 780 cm(-1). Thirty-two absorption lines were recorded for the isotopomer (35)ClCN and 26 lines for (37)ClCN. From the analysis of these lines, we determined the bandstrengths: S(0)(v) = 19.14 cm(-2) atm(-1) for (35)ClCN and S(0)(v) = 17.84 cm(-2) atm(-1) for (37)ClCN. Copyright 2000 Academic Press.

RESUMEN

Several infrared transitions of the nu(5) band of C(2)H(2) perturbed by Xe near 700 cm(-1) have been recorded using a tunable diode-laser spectrometer, equipped with a thermostatically regulated cell. The pressure and temperature regimes covered during the experiments are respectively ranging between 20 and 200 mbar and 170 and 350 K. The experimental profiles are accurately studied with a recently proposed lineshape model accounting for the collisional confinement narrowing of the Doppler spectral contribution, the inhomogeneous collisional broadening and shifting, and the exchange between the various speed classes of the Maxwell-Boltzmann distribution. The speed dependence of the collisional broadening is either ab initio calculated from a semiempirical potential or deduced from the experimental temperature dependence of the line broadening. It is shown that, for the considered range of temperature, this speed dependence does not significantly modify the lineshape, so that the usual hard and soft models conveniently account for most of the observed effects. Copyright 1999 Academic Press.

RESUMEN

N(2) broadening coefficients have been measured for 33 lines in the nu(3) fundamental band and 21 lines in the nu(3)-nu(1) band of C(32)S(2), using a tunable diode-laser spectrometer. These lines with J values ranging from 0 to 78 in the nu(3) band and from 4 to 70 in the nu(3)-nu(1) band are located in the spectral ranges 1514-1548 and 853-887 cm(-1), respectively. The collisional widths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. Semiclassical calculations of these broadening coefficients have been performed by considering, 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. Copyright 1999 Academic Press.

RESUMEN

By Fourier transform, spectra were recorded for carbon disulfide (12)C(32)S(2) in the region of weak absorption near 5200 cm(-1). The data were fitted and new molecular constants were determined. We also observed a band of the isotopomer (12)C(32)S(34)S. A self-broadening coefficient gamma(0) of 0.120 cm(-1). atm(-1) was obtained by recording two lines of the nu(3)-nu(1) band with a tunable diode laser. Copyright 1999 Academic Press.

RESUMEN

By diode-laser spectroscopy, spectra have been recorded for isotopically enriched carbon disulfide 13C32S2 in the region of the nu3 band near 1500 cm-1. The data were fitted and new molecular constants were determined. We also observed bands of isotopomers 13C32S33S and 13C32S34S. Copyright 1999 Academic Press.

RESUMEN

O2-broadening coefficients have been measured for 29 lines of C2H2 at 173.2 K in the P and R branches of the nu5 band near 14 µm, using a tunable diode-laser spectrometer. The collisional widths obtained by Rautian profiles closely fitting the measured spectral shape of the lines are slightly larger than those derived from Voigt profiles. The broadening coefficients are compared with results calculated from a semiclassical theory, performed by considering, in addition to electrostatic interactions involving the hexadecapole moments of C2H2 and O2, the atom-atom Lennard-Jones model. By comparing broadening coefficients at 297 and 173.2 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally and theoretically. Copyright 1999 Academic Press.

RESUMEN

The absolute strengths of 93 lines belonging to the nu2 and nu5 bands of methyl fluoride were measured in the range of 1416-1503 cm-1 using a tunable diode-laser (TDL) spectrometer. These experimental line intensities were obtained from the equivalent width method. The intensities were analyzed within a dyad system, required to account properly for the strong Coriolis coupling between nu2 and nu5. The fit to the experimental data led to the determination of the dipole moment derivatives partial differentialµ/ partial differentialq2 and partial differentialµ/ partial differentialq5, as well as the first-order Herman-Wallis correction in K to partial differentialµ/ partial differentialq5. The intensities were reproduced with an overall standard deviation of 1.44%, to be compared with a mean experimental uncertainty equal to 1.58%. The values derived for the vibrational band strengths of nu2 and nu5 are 2.124 (18) cm-2.atm-1 and 36.96 cm-2.atm-1 at 296 K, respectively. Copyright 1998 Academic Press.

RESUMEN

N2-broadening coefficients have been measured for 22 lines of C2H2 at 173.4 K in the P and R branches of the nu5 band, using a tunable diode-laser spectrometer. The lines with J values ranging from 1 to 29 are located in the spectral range of 661-762 cm-1. The collisional widths obtained by Rautian profiles fitting closely the measured spectral shape of the lines are slightly larger than those derived from Voigt profiles. Semiclassical calculations of these broadenings have been performed by considering, in addition to electrostatic interactions, successively the atom-atom model and the Tipping-Herman intermolecular potential. The results obtained, which for some of them are in good agreement with the experimental data, depend significantly on the isotropic potential used to describe the trajectory model. By comparing broadening coefficients at room and low temperature, their temperature dependencies have been determined both experimentally and theoretically Copyright 1998 Academic Press.

RESUMEN

Using a tunable diode-laser spectrometer, we have measured the O2-broadening coefficients for 45 lines of methyl fluoride in the QP and QR branches of the nu2 parallel band, and in the PP, PQ, PR, RP, RQ, and RR branches of the nu5 perpendicular band. These lines with J values ranging from 1 to 23 and K from 0 to 9 (K

RESUMEN

Ar-broadening coefficients are measured for 29 lines of CH3F in the RQ0 and RQ6 branches of the nu6 band, using a tunable diode-laser spectrometer. The collisional widths obtained by fitting Rautian profiles to the measured shapes of the lines are significantly larger, especially for the overlapping lines at low-J values, than those obtained from Voigt profiles. The broadening coefficients for the lines belonging to the same low-J transitions (J = 7-10) appear to be greater in the RQ0 branch than in the RQ6 branch. Comparisons have been made with calculated results based on a semiclassical model including adjustable potential parameters. Copyright 1998 Academic Press.

RESUMEN

The 14 transitions belonging to the P branch of the nu3 band of CH3D, near 1250 cm-1, have been measured with a tunable diode-laser spectrometer. These lines, recorded at a total pressure ranging from 1 to 60 mbar, have been analyzed by means of soft and hard collision lineshape models. We emphasize the equivalence between the correlated and noncorrelated profiles, when the collisional lineshift may be neglected. As a result, new measurements of linestrengths, collisional self-broadening coefficients, and other parameters related to the Dicke effect are provided at room temperature. It is also shown that the instrumental distortions must be properly taken into account to avoid systematic errors on the fitted lineshape parameters, especially at low pressure. The broadening coefficients are compared with results calculated from a semiclassical theory, performed by considering, in addition to electrostatic interactions involving the octopole and hexadecapole moments of CH3D, the dispersion contributions. Copyright 1998 Academic Press.

RESUMEN

Three infrared absorption lines of the nu5 band of C2H2 diluted by Xe at pressures ranging from 40 to 300 mbar have been recorded at high resolution near 750 cm-1, using a tunable diode-laser spectrometer. Their lineshapes have been first analyzed by means of models using either the Dicke narrowing effect or the absorber speed-dependent collisional broadening and shifting. None of these models have given satisfactory results over the full pressure range of the perturber. It is shown that a correct treatment must include both line narrowing effects. We have investigated two possibilities of doing so: a convolution between two profiles corresponding to each effect and a noncorrelated and speed-dependent Rautian profile that we have developed here. The latter lineshape model appears to be the most appropriate. Copyright 1997 Academic Press. Copyright 1997Academic Press

RESUMEN

The strengths of 100 lines in the 2nu3 band of 16O12C32S have been measured at high resolution in the spectral range 4069-4118 cm-1, using a tunable difference-frequency laser spectrometer. These intensities were obtained by fitting Voigt profiles to the measured shapes of the lines. The vibrational transition moment [(2.141 ± 0.020) x 10(-2) D] and the absolute intensity (16.19 ± 0.24 cm-2 atm-1 at 296 K) of the 2nu3 band of 16O12C32S are determined from these linestrength measurements. Copyright 1997 Academic Press. Copyright 1997Academic Press

RESUMEN

The hot bands accompanying the fundamentals nu6 and nu3 of CH3NC in the region 1300-1560 cm-1 observed in high-resolution Fourier transform recordings complemented by diode laser spectra have been analyzed. The observed transitions comprise 16 subbands of the pair of perpendicular E-E bands nu6± + nu8± - nu8± and nu7-/+ + 2nu80 - nu8± whose upper states form a Fermi dyad, 18 subbands of the A1,2-E perpendicular bands nu6-/+ + nu8± - nu8±/nu7± + 2nu8±2 - nu8± with upper states forming another Fermi dyad, and 8 subbands of the bi-parallel E-E band nu3 + nu8± - nu8±. The anharmonic, Coriolis, and l-type interactions which couple these upper states with each other and with the states nu7-/+ + 2nu8±2, nu4 + 3nu8±1, and nu4 + 3nu8±3 have been included in an 18 x 18 Hamiltonian matrix whose eigenvalues model the upper levels of the observed transitions. The values of 46 upper state spectroscopic constants and interaction constants have been adjusted by least squares to 950 observed lines. The results provide a reliable quantitative picture of the interacting states and yield accurate values for the spectroscopic constants of the various states and for the anharmonic constants x68, x68 (g68), and x38. Copyright 1997Academic Press

RESUMEN

He-broadening coefficients are measured for 28 lines of 12CH3F in the RQ0 (Ki = 0, DeltaK = 1, DeltaJ = 0) and RQ6 (Ki = 6, DeltaK = 1, DeltaJ = 0) branches of the nu6 band, using a tunable diode laser spectrometer. The collisional widths obtained by fitting Rautian profiles to the measured shapes of the lines are slightly larger than those derived from Voigt profiles. The broadening coefficients for the lines belonging to the same low J transitions are significantly greater in the RQ0 branch than in the RQ6 branch. Moreover, they decrease on the whole with increasing J in the RQ0 branch and tend to increase from J varying from 7 to 10 in the RQ6 branch. These trends may be approximately reproduced by calculations based on a semiclassical impact theory of collisional broadening. Copyright 1997 Academic Press. Copyright 1997Academic Press

RESUMEN

A theoretical model based on the energy corrected sudden (ECS) approximation is used in order to account for line-mixing effects in Delta left and right arrow Pi infrared Q branches of 12C16O2. Its quality is demonstrated by comparisons with numerous laboratory spectra of CO2-He and CO2-N2 mixtures: three Q branches in the 4 and 17 µm regions are investigated at room temperature in a wide pressure range. The influence of mixing between Q(J) lines associated with odd and even values of the rotational quantum number J is demonstrated and analyzed in detail. It is shown that, in contrast to available fitting law approaches, the ECS model correctly predicts the influence of the parity of the rotational quantum numbers J and J' on coupling between the Q(J) and Q(J') lines. Comparisons between the effects of collisions of CO2 with N2 and He are made and analyzed. They show that these two systems involve different line couplings within the Q branch. Copyright 1997 Academic Press. Copyright 1997Academic Press