Jacques Walrand

Lineshapes and broadening coefficients in the v5 band of C2H2 in collision with Kr and He

Abstract General Voigt profiles (GVPs), including the speed dependence of collisional cross-sections, have been fitted to the following measured spectral lineshapes: the shapes of the R(7), R(11) and R(14) lines recorded with a tunable diode-laser spectrometer in the v5 band of C2H2 in collision with He and Kr. The various GVPs and the resulting broadening coefficients are almost identical for light pertubers such as He and depend significantly on a simplified form in r-q of the interaction potential for heavy pertubers such as Kr. We consider three GVPs with q = 3 (Voigt function), q = 6 and q = 12, as well as the Galatry profile incorporating Dicke narrowing associated with velocity-changing collisions. The speed-dependent Voigt profile with q = 6 provides generally closer agreement with the spectral data of C2H2-Kr than the other GVPs and leads to Kr-broadening coefficients that are nearly 5% larger than those derived from the conventional Voigt profile.

Self-broadening coefficients and line strengths in the v3 band of CH335C1 at low temperature

Abstract Self-broadened linewidths have been measured in the P- and R-branches of the v 3 band of CH 3 35 Cl at 200 K using a tunable diode-laser spectrometer. The lines under study are located in the spectral range 706–751 cm -1 , with J values ranging from 3 to 27 and K from 3 to 6. The collisional half-widths were estimated along with the corresponding line strengths by fitting measured shapes of the individual lines with Voigt profiles convolved with the instrumental function. The line strengths at 200 K are in satisfactory agreement with results derived from previous measurements. Even though semi-classical calculations of line-broadening involving electrostatic interactions have yielded half-widths at 200 and 296 K that are greater than experimental data for low or medium values of J , they seem to predict correctly the K -dependence of the broadening coefficients of lines with the same J transition as well as their temperature dependence.

H2-broadening coefficients in the ν2 and ν4 bands of PH3

Abstract H2-broadening coefficients are measured for 41 transitions of PH3 in the Q R branch of the ν2 band and the P P , R P , and P Q branches of the ν4 band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 2 to 16 and K from 0 to 11 are located between 995 and 1106 cm −1 . The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. These coefficients γ0(J,K) are found to decrease slightly on the whole as J increases and they decrease significantly for K values approaching or equal to J (J⩾4) . The H2-broadenings are also calculated on the basis of a semiclassical model of interacting linear molecules, using an atom–atom Lennard-Jones potential in addition to the weak electrostatic contributions. The theoretical results are in satisfactory agreement with the experimental data and reproduce the J and K dependencies of the broadenings, but the decrease observed for the Q R(J,K) transitions with K=J is notably overestimated.

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

Abstract 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|

Diode-laser measurements of collisional line broadening in the v5 band of C2H2

Abstract Self-broadening coefficients for 27 lines of acetylene in the P - and R -branches of the v 5 band have been measured at room temperature with a tunable diode-laser spectrometer. We have first calculated these broadening coefficients on the basis of two semi-classical impact models by using a simple intermolecular potential. The quadrupole moment of C 2 H 2 as well as a dispersion parameter have then been determined by fitting the calculated results of our experimental data. We next use the approach of Robert and Bonamy in which the intermolecular potential does not include adjustable parameters and involves the addition of an atom-atom interaction model to the electrostatic interactions. The usual spherical harmonics expansion of the atom-atom potential appears to be quite inadequate at short distances. The results of calculations derived from a rough consideration of the exact radial expansion of the atom-atom potential lead to better agreement for high J lines than those derived from the truncated expansion. It is also shown that the electrostatic contributions arising from the hexadecapole moment of C 2 H 2 are only significant for | m | > 20.

Diode-laser measurements of carbon disulfide and general rovibrational analysis

Abstract By using a tunable diode-laser spectrometer, six transitions have been observed in the ν 3 − ν 1 region of 12 C 32 S 2 . One band of 12 C 32 S 34 S has been analyzed. The molecular constants of 12 C 32 S 2 have been determined by a general rovibrational analysis including all known data.

Diode-laser measurements of Ar- and CO2-broadened linewidths in the v1 band of OCS

Abstract The pressure-broadening coefficients for a number of spectral lines ranging from| m | = 1to 58 in the v 1 band of 16 O 12 C 32 S, have been measured for collisions with Ar and CO 2 with a tunable diode-laser spectrometer. The results are compared with values calculated on the basis of the Anderson-Tsao-Curnutte theory and an improved semi-classical impact theory. For OCS-Ar, we have used the Tipping-Herman intermolecular potential, as well as an atom-atom interaction model. For OCS-CO 2 , we have considered, in addition to electrostatic interactions, successively a simple formalism for the anisotropic dispersion forces and the atom-atom interactions.

Line-mixing effects in N2O Q branches: Model, laboratory, and atmospheric spectra

A model based on the energy corrected sudden approximation is used in order to account for line-mixing effects in N2O Q branches of Σ↔Π bands. The performance of this theoretical approach is demonstrated by comparisons with many (about 70) N2O–N2 and N2O–O2 laboratory spectra recorded in the 5 and 17 μm regions by three instrument setups; the Q branches of the 2ν20e–ν21f (near 579.3 cm−1), ν2 (near 588.8 cm−1), and ν2+ν3 (near 2798.3 cm−1) bands are investigated for different pressures (0.1–2.0 atm) and temperatures (200–300 K). The model is used to generate a set of line-mixing parameters for the calculation of the absorption by the ν2 Q branch under atmospheric conditions. These data are tested by comparisons between computed stratospheric emissions and values measured using a balloon-borne high resolution Fourier transform instrument. The results confirm the need to account for the effects of line mixing and demonstrate the capability of the model to represent the N2O absorption in a region which can b...

Diode laser spectroscopy of methyl chloride near 14 μm toward its detection in the stratosphere

Abstract Detection of CH 3 Cl in the Earths atmosphere by infrared techniques is a subject of current interest. The ν 3 band, centered at 732 cm −1 , has lines as strong as those of ν 1 , centered at 2970 cm −1 , and we show that they can be useful for a high-resolution detection. A complete study of the absorption spectrum of this molecule in the region 660–770 cm −1 has been performed. On spectra recorded using a tunable diode laser spectrometer, with the spectral resolution limited by the Doppler width (0.0014 cm −1 ), we have assigned the ν 3 band lines related to four isotopic species: 12 CH 3 35 Cl, 12 CH 3 37 Cl, 13 CH 3 35 Cl, and 13 CH 3 37 Cl. In addition, the hot band 2 ν 3 - ν 3 for 12 CH 3 35 Cl has been observed. The calculated molecular constants reproduce, for each band, the observed wavenumbers with a rms deviation of 6 × 10 −4 cm −1 . The ν 3 band centers have been found to be 732.8421 and 727.0295 cm −1 for the two main isotopic species, 12 CH 3 35 Cl and 12 CH 3 37 Cl, respectively. The feasibility of detection of methyl chloride in the stratosphere is discussed.

Diode-Laser Measurements of N2-Broadening Coefficients in the ν3 Band of CH3D

Abstract N 2 -broadening coefficients have been measured for 33 lines of 12 CH 3 D in the Q P and Q R branches of the ν 3 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 than those derived from Voigt profiles. Semiclassical calculations of the broadening coefficients have shown the importance of the nonelectrostatic contributions in the anisotropic intermolecular potential.