The gas-phase spectrum of BH3 was detected for the first time by diode laser spectroscopy through the observation of the ν2 band. The borane was produced by photolysis of B2H6 or BH3CO with an ArF excimer laser. The same spectrum was obtained by a discharge in a B2H6 and He mixture. Line assignments were made for the Q-branch series with J=K of the ν2 band; effects due to Coriolis perturbations by the ν4 state were recognized.
Collision cross sections for the transverse relaxation of OCS by spherical and nearly spherical perturbers have been measured. The observed cross sections vary linearly with β=[I22/(I1+I2)2α22M]1/5, where I1 and I2 are the ionization energies of OCS and the perturber. α2 is the polarizability of the perturber, and M is the reduced mass of the colliding molecules. Calculations based on the Anderson–Tsao–Curnutte theory using a simple dispersion force model for the OCS–perturber interaction are in qualitative agreement with the experimental results. By doubling the strength of the dispersion forces used to model the OCS–perturber interactions, the calculated cross sections are brought into agreement with the measured ones. The observed linear relation between the cross section and β can be used to predict cross sections for other (polar molecule)–(nonpolar nearly spherical perturber) collisions.
Recently an acoustic destabilizing pressure was predicted, which could be shown experimentally via a dewetting pattern in thin polymer films. The wavelength λ of the fastest growing mode is a signature of the acting forces. Even in cases with stabilizing van der Waals forces, films became unstable. The present paper also considers thermally excited acoustic waves confined in a thin liquid film of thickness d. A new concept is developed to calculate the acoustic pressure for different boundary conditions: the free-standing film, the film rigid at one surface and the film deposited on a substrate, liquid or solid. For characteristic examples the calculation is carried out numerically. The results for the limiting cases are simple. The acoustic pressure of the free-standing film grows monotonically with d up to a level strongly depending on the temperature, it cannot destabilize the film. The acoustic pressure of the film rigid at one surface rapidly grows with d to a maximum and then decreases monotonically to the same level as for the free-standing film. On the right side of the maximum the film is unstable and λ grows quadratically with d, similar to the case of a destabilizing van der Waals pressure. For a film deposited on a substrate the acoustic pressure comes to a smaller level directly, depending on the excess sound velocity in the substrate: generally it yields a rather linear dependence of λ on d.It was derived by Schäffer et al [6] using the same energy k B T for all states and the Debye approximation for a free-standing
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