Conformational relaxation paths in tryptamine.

The relative fluorescence intensities of three conformers of tryptamine have been determined as a function of stagnation pressure and nozzle temperature in a supersonic expansion. The relative intensities of the conformers that are connected by different direct and indirect interconversion paths on the potential-energy hypersurface differ considerably depending on the experimental conditions. The energies of the local minima and some transition states interconnecting them are studied on the ab initio level of theory. From the energies of the barriers and vibrational frequencies at the stationary points, conformer interconversion rates k(T) and k(E) have been obtained using statistical theories. In the cases experimentally observed here, vibrational cooling rates and interconversion rates must be of the same order of magnitude, while RRKM theory considerably overestimates k(E) values, most probably due to an insufficient consideration of anharmonic coupling of the vibrational modes in tryptamine.