Hyperfine effects on collisional line shape. I. A self-consistent set of equations.

We show that the treatment available in the literature for calculating hyperfine effects on collisional line shape is affected by an error making the theory not self-consistent. By correcting such an error we show that the two hyperfine effects on the line shape, modification of the resolved components and collisional coupling between them, cancel each other when hyperfine structure collapses into a single line.

Hyperfine effects on spectral line shape. II. The case DCO+-He.

We discuss the hyperfine effect on the shape of rotational spectral lines of DCO(+) broadened by collisions with helium. Hyperfine scattering matrix is calculated by the recoupling technique from the spin-free scattering matrix which is obtained by close-coupling calculations and by a previously tested potential. Line shape is calculated for different rotational transitions, perturber density values, and collisional energies. As forecast by a semiclassical treatment and contrary to what may happen for a symmetric top absorber, hyperfine effects are small for a linear absorber. In our case they are of about 2%. We could also verify that the two hyperfine effects on the line shape, modification of resolved components and collisional coupling between them, cancel each other at high values of helium density when hyperfine structure collapses into a single line.

Hyperfine Level Dependence of the Pressure Broadening of CH(3)I Rotational Transitions in the v(6) = 1 Vibrational State.

We studied the hyperfine components of the (J = 10-9, Kl = 9) rotational transition in the v(6) = 1 excited vibrational state of CH(3)I, using collinear infrared and mm-wave radiations. The Doppler-free double-resonance technique allowed an accurate determination of the collisional broadening parameters for all the hyperfine components. An evident dependence on the F quantum number was observed and this result is perfectly consistent with a theoretical model allowing calculations of collisional broadening and coupling for the hyperfine components. Copyright 2000 Academic Press.

Ammonia spectrum as a test for two different pressure shift theories.

Pressure shift calculations, based on the semiclassical ATC theory and on the quantum Fourier transform (QFT) theory, are compared wtih experimental results for seventy-two inversion, rotation, and vibration transitions of (14)NH(3) and (15)NH(3). ATC, even if not exact, allows a far better agreement than QFT. A possible reason for this is briefly discussed.

Predictions for collisional broadening of far-infrared OH rotational lines of atmospheric interest.

Collisional line shapes for OH in the presence of N(2) are computed using the Anderson theory. The theoretical results compare satisfactorily with the experimental results now available. Predictions for all strong OH farinfrared lines are given together with the dependence of broadening and shift on temperature. The results will be useful in the interpretation of atmospheric or astrophysical spectra.