The torsional spectra of jet-cooled methyl substituted indoles in the ground and first excited states

We have analyzed the jet-cooled torsional spectra of the S1–S0 transitions for the seven monomethyl indoles. The potential curves which describe the hindered internal rotation in both the ground and excited states are modeled with the form: V(φ)= 1/2 ∑n Vn(1−cos nφ). The changes in the torsional potential upon electronic excitation can be interpreted as arising from changes in the electron density adjacent to the methyl rotor. We present evidence that the methyl rotor is then a unique probe with which to obtain information about the detailed electronic structure of the parent indole molecule. This approach provides new evidence for the assignment of the first excited electronic state of indole observed in the vapor phase to 1Lb.