1La origin locations of methyl indoles in argon matrices

Polarized fluorescence excitation and dispersed fluorescence spectra of 3-methylindole (3MI), 5-methylindole (5MI), and 2,3-dimethylindole (2,3DMI) in solid Ar at 20 K under site selective conditions have unambigously revealed their 1La origin locations. For 3MI the 1La origin is 260 cm−1 above the 1Lb origin and for 5MI it is 1800 cm−1 above 1Lb. For 2,3DMI, the 1La origin lies 190 cm−1 below the 1Lb origin. The latter assignment is made from details of the dispersed fluorescence in comparison to the phosphorescence spectrum of indole in argon at 20 K.