The vibrationally resolved mass analyzed threshold ionization spectra of jet-cooled 1-methylindole (1MI) have been recorded by ionizing via four vibronic levels. The adiabatic ionization energy of this molecule is determined to be 60 749 +/- 5 cm(-1), which is less than that of indole by 1842 cm(-1). This indicates that the N-methyl substitution causes a greater extent of the lowering in the zero energy level of the cationic ground state than that of the neutral. A few characteristic vibrations of the 1MI cation are observed, where the frequencies of the out-of-plane, in-plane bending and stretching vibrations of the N-CH3 part are found to be 124, 251, and 1492 cm(-1), respectively. (C) 2003 Elsevier B.V. All rights reserved.