O. Tarrini

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‐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.

Ammonia inversion spectrum: detailed measurements and theoretical calculations of pressure shift

The pressure shift of some ammonia inversion lines has been measured by a modified double-modulation spectrometer. Due to some unique features, a substantial improvement in stability and frequency resolution has been obtained over previous measurements. The experimental results have been compared with values deduced from an extension of Andersons theory. There is an order of magnitude agreement and possible causes of discrepancy are discussed.

Temperature dependence of foreign gas broadening and shift of the aQ(9,9) transition line of ammonia

N2, Air, O2, H2, Ar, and He broadening and shift of the aQ(9,9) transition line of ammonia have been measured in the temperature range 180–380 K with errors of ∼2 and 10%, respectively. All the measurements have been fitted with the well-known power law, which holds very well in the temperature range considered here. N2 pressure effects have also been compared with calculations based on the Anderson–Tsao–Curnutte (ATC) theory with mixed results, anyway much more satisfactory for broadenings than shifts.

Experimental and Theoretical Study of the Broadening and Shifting of N2H+ Rotational Lines by Helium

Pressure broadening and pressure shift of N(2)H(+) rotational lines perturbed by collisions with He are studied for the first time using experiment and theory. Results are reported from measurements at 88 K for the rotational transitions j = 3<--2, 4<--3, 5<--4 and 6<--5 with frequencies ranging from 0.28 to 0.56 THz. The agreement between experiment and theoretical data derived from close coupling calculations confirms the reliability of a theoretical framework used for state-to-state transition rates of interest in the interpretation of spectroscopic data from interstellar molecular clouds. The influence of hyperfine effects on shifts and widths of the rotational lines is discussed in detail. Although in principle possible, experiment and theoretical considerations lead to the conclusion that hyperfine effects only play a minor role.

H2O-H2O Collision Rate Coefficients

H2O-H2O collision cross sections are calculated by adapting the method developed by Anderson and Tsao and Cornette for the calculation of collision broadening of molecular spectral lines. Cross sections are computed with a cutoff limit at 20 A2 for the rotational levels of water with J ≤ 10 and E < 2000 cm-1 in the temperature range 100-800 K. The accuracy of the calculated values is estimated to be 10%-20%.

Broadening of CH3F in presence of Stark fields. I. Self-broadening and self-shifting of isolated components

Self-broadening and shifting of methyl fluoride 12CH3F have been investigated in the 50–408 GHz range for the rotational transitions J=0→1, J=1→2, J=2→3, J=5→6, and J=7→8 and for their ΔM=0 and ΔM=±1 Stark components, as they were resolved by an appropriate field. The different results obtained for M-degenerated and M-resolved cases, as well as the M dependence of the results has been interpreted theoretically within semiclassical perturbative approximations. Evidence of collisional coupling effects between Stark components was obtained.