G. Buffa

Experimental and theoretical investigation of self‐broadening and self‐shifting of ammonia transition lines in the ν2 band

We have measured self‐broadenings and self‐shiftings of several rotovibrational transitions of the ν2 band of NH3. We have found smaller broadenings and bigger shifts with respect to the known data of the inversion spectrum in the microwave region. The experimental results are compared with the Anderson original line broadening theory, successively extended in order to calculate the shift also. The agreement between experiments and theory is quite good so that it is possible to select the right procedure among those usually adopted in order to avoid divergences occurring in the Anderson’s perturbative treatment of the molecular collision matrix.

N2, O2, H2, Ar and He broadening in the ν1 band of NH3

Abstract N 2 -, O 2 -, H 2 -, Ar- and He-broadening coefficients and pressure shifts have been measured for Q - and R -branch transitions in the ν 1 fundamental band of ammonia using a difference-frequency laser spectrometer. The J - K dependence of the broadening coefficients is much smaller than previously observed for self broadening of NH 3 . Semiclassical line broadening calculations for N 2 broadening are in reasonable quantitative agreement with the data, but they also exaggerate the J - K dependence. Dicke narrowing is observed as strong deviations from Voigt profiles at intermediate pressures and provides estimates for optical diffusion constants which correlate well with the mass diffusion constants for NH 3 in the various buffer gases.

Self broadening in the v1 band of NH3

Abstract Self-broadening coefficients, pressure shifts and integrated intensities have been measured for Q- and R-branch transitions in the v1 fundamental band of ammonia using a difference-frequency laser spectrometer. A strong, systematic J and K dependence of the broadening coefficients, reminiscent of the ground-state inversion transitions, is observed and compared with semiclassical line broadening calculations. Dicke narrowing is evident at intermediate pressures for the sharpest lines, primarily the R(J, 0) transitions. Incipient line mixing is apparent in the Q branch at pressures above ∼0.1 bar.

Foreign-gas pressure broadening and shift of ammonia transition lines in the ν2 vibrational bands

Abstract Foreign-gas broadening and shift have been measured for transitions in the ν2, 2ν2 and ν4 bands of ammonia using a diode laser spectrophotometer. The measurements were performed by using foreign-gases such as CO2, N2, air, H2, and He at room temperature. The pressure-broadening and shift coefficients may be useful in modelling planetary atmospheres and the recently developed infrared (i.r.) ammonia laser. The experimental results are compared with the Anderson-Tsao-Curnutte theory for broadening CO2 and N2, which have large quadrupole moments. The agreement is satisfactory on the average.

Self‐broadening and self‐shifting of ammonia lines in the 2ν2 band

We have measured pressure broadening and shifting of some transition lines of ammonia 14NH3 in the 2ν2 band. The agreement between the experimental results and the Anderson theory is satisfactory. We also discuss the possibility of obtaining the value of the dipole moment in the ν2=2 vibrational state from pressure broadening data.

Self‐broadening and self‐shifting of ammonia lines in the 2ν2 band around 16 μm

We have measured the pressure broadening and shift of several transition lines of ammonia, 14NH3, in the 2ν2 band around 16 μm. Satisfactory agreement is found between the experimental results and a slightly modified version of the Anderson theory. A comparison between the theory and measurements of other authors has also been made.

Toward a Complete Understanding of the Vinyl Fluoride Spectrum in the Atmospheric Region

A deep and comprehensive investigation of the vinyl fluoride (CH(2)CHF) spectrum in the atmospheric window around 8.7 μm is presented. At first, the ro-vibrational patterns are modelled to an effective Hamiltonian, which also takes into account the coupling of the C-F stretching vibration, ν(7), with the neighbouring vibrational combination ν(9)+ν(12). The obtained Hamiltonian gives very accurate simulations and predictions of the ro-vibrational quantum energies. Then, in the main part of the work, an experimental and theoretical study of vinyl fluoride self-broadening collisions is carried out for the first time. The broadening coefficients obtained experimentally are compared with those calculated by a semiclassical theory, demonstrating a significant contribution of collisional coupling effects between lines connecting pairs of degenerate (or nearly degenerate) rotational levels. Finally, the experimentally retrieved integrated absorption coefficients are used to calculate the absorption cross-section of the ν(7) normal mode, from which dipole transition moments are derived. The obtained results provide a deep insight into the spectral behaviour of vinyl fluoride, in a spectral region of primary relevance for atmospheric and environmental determinations. Indeed, the data presented constitute an accurate model for the remote sensing of vinyl fluoride--a molecule of proved industrial importance which can lead to hazardous effects in the atmosphere and affects humans health.

Spectroscopic measurements of SO2 line parameters in the 9.2 μm atmospheric region and theoretical determination of self-broadening coefficients

Sulfur dioxide is still the subject of numerous spectroscopic studies since it plays an active role in the chemistry of Earths atmosphere and it is a molecule of proven astrophysical importance. In the present work we have determined the self-broadening and integrated absorption coefficients for several lines in the nu(1) band spectral region around 9.2 mum. Besides the parameters of the lines belonging to the nu(1) fundamental of (32)SO(2), also those for some rovibrational lines of the nu(1)+nu(2)-nu(2) hot band of the (32)SO(2) isotopologue and the nu(1) band of the (34)SO(2) isotopic species have been determined. The measurements have been carried out at 297 K using a tunable diode laser spectrometer. The self-broadening parameters have also been theoretically determined employing a semiclassical formalism based on the Anderson-Tsao-Curnutte approximation. The study has been completed with the determination of the vibrational cross sections of the three fundamental bands measured from the spectra recorded at a resolution of 0.2 cm(-1) using a Fourier transform infrared spectrometer.

Self‐collisional coupling and broadening in the asymmetric rotor CHF2Cl

The line shape of 15 selected CHF2Cl rotational transitions is studied in the 59–1049 GHz frequency region. Collisional broadening parameters are measured and compared to semiclassical calculations. For some pairs of lines a large collisional coupling effect is observed and analyzed. A semiclassical theoretical model is presented allowing calculations of the coupling parameters in good agreement with measurements.

A review of experiments and theory for collisional line shape effects in the rotovibrational ammonia spectrum

Summary455 self-broadening, self-shift and foreign gas (N2 and CO2) broadening measurements forv2 andv4 ammonia vibrational bands are compared to theoretical calculations performed in the frame of the semi-classical impact approximation. On the whole the agreement is satisfactory. However, a detailed analysis of the experimental and theoretical results shows some shortcomings in the accuracy of the experimental data and in the validity of the theoretical approach. General indications are given in order to improve further the description of the collisional line shape effects which is of great interest both for basic knowledge and for various applications.