Direct measurement of energy thresholds to conformational isomerization in tryptamine.

Stimulated emission pumping (SEP)-hole filling spectroscopy and SEP-induced population transfer spectroscopy have been used to place narrow bounds on the energy thresholds for isomerization between individual reactant-product isomer pairs involving the seven conformational minima of tryptamine. The thresholds for isomerizing conformer A to all six other conformations divided into three groups at 750 wavenumbers (cm-1)(A-->B, F), 1000 cm-1 [A-->C(2)], and 1280 to 1320 cm-1 [A-->D, E, and C(1)]. The appearance of the first band and the absence of the band below it were used to place upper and lower bounds to the barrier heights for each process. The thresholds for A-->B and B-->A isomerizations were also combined to determine the relative energies of these two lowest energy minima. The combined data from all X-->Y isomerizations identify important isomerization pathways on the potential energy surface linking the minima.