Jean-Pierre Bouanich

Site-site lennard-jones potential parameters for N2, O2, H2, CO and CO2

The classical second-virial coefficients B(T) for identical linear molecules have been calculated exactly by using a potential model that includes site-site Lennard-Jones 12-6 interactions with added dipole and quadrupole interactions. By fitting selected experimental values of B(T) and using up to three different plausible quadrupole moments of the molecules, we have determined site-site Lennard-Jones parameters for N2, O2, H2, CO and CO2. We have also considered, in addition to electrostatic interactions, a limited spherical harmonics expansion of the site-site potential. By using at short range only the isotropic part of this expansion, we have derived parameters that are close for N2, O2 and H2 to the exact site-site parameters. The validity of this approximation in the truncated site-site potential is more questionable for CO and CO2.

Pressure induced shifts of CO2 lines: Measurements in the 0003–0000 band and theoretical analysis

Self‐broadened and N2, Ar, He‐broadened halfwidth and pressure shift coefficients of the rotational transitions in the 0003–0000 band of 12C16O2 have been measured from laboratory absorption recorded at room temperature with a Fourier transform spectrometer. Comparison is made with the results of a theoretical calculation based on a semiclassical model. Good agreement is obtained for all the IR vibrational bands for which data are available. It has been shown that the shifts mainly originate from vibrational dephasing. Infrared line shifts have been compared with results obtained from stimulated Raman spectroscopy and we show that they are not consistent. A number of possible explanations have been discussed to account for this discrepancy.

N2- and O2-broadening coefficients of C2H2 IR lines

Abstract Pressure-broadening parameters of six lines belonging to the ν 5 band of C 2 H 2 in collision with N 2 have been measured with a tunable diode-laser spectrometer in order to complete up to J = 33 our earlier measurements (D. Lambot, G. Blanquet, and J. P. Bouanich, J. Mol. Spectrosc. 136 , 86–92 (1989)) on the broadening of C 2 H 2 by N 2 and O 2 at 297 K. These N 2 - and O 2 -broadening coefficients have been first calculated on the basis of the Anderson-Tsao-Curnutte theory; in this approach, we show that the short-range interactions which contribute significantly to the linewidths are not correctly treated. Next, we consider the improved semiclassical model proposed by Robert and Bonamy. The intermolecular potential consists in the addition of the atom-atom interaction model to the quadrupolar interactions. The limited radial spherical harmonics expansion of the atom-atom potential, from which expressions for the differential cross section were derived, appears to be quite insufficient at short intermolecular distances. Therefore, we use a more accurate representation of this potential, avoiding an inadequate truncation and keeping the analytic expressions obtained by Bonamy and Robert. In the calculations we take into account the contributions derived from the radial functions U 000 ( r ), U 200 ( r ), and U 220 ( r ), as well as from U 400 ( r ). A theoretical expression is obtained for the U 400 contribution to the differential cross section. The results of the calculations arising from the exact radial expansion of the atom-atom potential appear to be significantly larger for high J lines than those arising from the truncated expansion. The latter results, which do not include adjustable atom-atom parameters, are in good agreement with experimental broadening coefficients for C 2 H 2 O 2 and in reasonable agreement (except at large J values) for C 2 H 2 N 2 . It is also shown that the contributions to the linewidths derived from U 400 are rather small for C 2 H 2 N 2 and more important for C 2 H 2 O 2 . Finally, by calculating the collisional linewidths of C 2 H 2 N 2 and C 2 H 2 O 2 at 200 K, we have predicted their temperature dependences.

Shifting and broadening in the fundamental band of CO highly diluted in He and AR: A comparison with theory

We present measurements of the shifts and widths of the rovibrational lines of the fundamental band of CO highly diluted in He and Ar at 296 K. The shifts are decomposed into parts odd and even in the line number, m. These are then compared with close coupled calculations carried out with the best known interaction potentials. There is general agreement between the calculated and measured values of the broadening and shifting. Furthermore, the results illustrate that the decomposition of the shifts into parts, odd and even in m, is a powerful tool for separating out the relative contributions of the isotropic and anisotropic part of the interaction to the shifts and which part needs to be corrected if there is a discrepancy. Thus, shift measurements can be added to the list of experiments that may be used to determine reliable interaction potentials. The results also show, given a potential, that close coupled calculations are accurate and could be used to confirm or establish empirical models of the temperature dependence of the broadening or shifting, etc. Such modeling is important at atmospheric physics.

Higher-order contributions to the Dunham coefficients; Application to the ground state of CO

Abstract The Dunham coefficients Y ij have been expanded through the eighth-order contributions and for some coefficients through the tenth-order contributions. The formalism obtained has been applied to an analysis of the ground electronic state of 12 C 16 O. From the most recent spectroscopic data, it was not possible to deduce reasonable values for the potential energy coefficients a i i >6.

Linewidths of carbon monoxide self-broadening and broadened by argon and nitrogen

Abstract Linewidths of CO pressure-broadened by itself and by foreign gases have been measured in the fundamental and the 0–3 bands. Andersons theory, in which we have included recent developments concerning the intermolecular potential and the perturber trajectories, has been applied to compute these linewidths. A comparison of theoretical results with experimental data suggests that the problem of short-range interactions has not been resolved satisfactorily.

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.

Determination of broadening coefficients and intensities for overlapping spectral lines with application to the QR (3,K) lines in the v3 band of CH353Cl

Abstract We have developed a method of extracting individual line parameters from overlapping absorption spectra recorded with a tunable diode-laser spectrometer. Assuming Voigt profiles for the individual lines, the overall absorption is expressed as the sum of the absorption coefficients of the recorded lines plus a small contribution due to neighboring lines. The computational procedure has been applied to the four Q R (3, K ) lines, self-broadened and broadened by N 2 ,O 2 , Ar and He, in the v 3 band of CH 35 3 Cl at 736.3 cm -1 . The intensities and collision-broadened widths are found to be linear functions of the broadener pressures, which implies negligible line-mixing effects between the K components. For all the perturbers considered the broadening coefficients of the Q R (3, K lines decrease significantly as K increases, in agreement with theoretical results.

Diode laser measurements of collisional broadening in the ν5 band of C2H2 perturbed by O2 and N2

Abstract O 2 - and N 2 -broadening coefficients for a number of acetylene lines in the P and R branches of the ν 5 band have been measured at room temperature with a tunable diode laser spectrometer. From these results, air-broadening coefficients have been deduced, using the additivity property of the broadening coefficient.

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.