Contribution Contributed Talk
Collision induced transitions of ammonia revisited
The Chirped-Pulse Fourier Transform Spectrometer (CPFTS) at the CAS laboratories at MPE has been used to revisit the microwave studies of collision induced transitions between rotational levels of ammonia done by T. Oka (J. Chem. Phys. 48, 4919 (1968)) in order to study the capabilities of the CPFTS to derive important constraints on collisional rates. Selected inversion doublets have been 'pumped' and the change in population in other inversion doublets induced by the pump pulse has been probed.
In contrast to the steady-state measurements by Oka, the time-resolution of the CPFTS allows to probe the population of inversion doublets as a function of delay time between pump and probe pulse and thus to follow how the population relaxes back to thermal equilibrium. Collisional rates have been fitted to reproduce the experimental data. The current status and preliminary results of this ongoing project will be presented.