Slow electron velocity-map imaging (SEVI) has been employed for the ionization spectroscopic study of the jet-cooled 5-methylpyrimidine in the first singlet (1)(n pi*) excited state. Resonant-enhanced two-color two-photon (1 + 1') ionization spectrum gives well-resolved S-1 vibrational structures up to similar to 2400 cm(-1) above the origin whereas spectral bands becomes completely broadened in the higher energy region as coupling of individual S-1 bands to dark states becomes significant. Ionization of the S-1 5-methylpyrimidine with different ionization wavelengths at several different delay times reveals the property of low-lying (3)(pi pi*) triplet dark state which is prepared by fast nonadiabatic transition. SEVI spectra taken via various S-1 intermediate states provide the detailed vibrational structures of the 5-methylpyrimidine cation (D-0), also giving the adiabatic ionization energy of 9.1052 +/- 0.0030 eV (73 438 +/- 24 cm(-1)). Geometrical changes in the S-0-S-1-D-0 transitions are discussed from Franck-Condon simulations based on calculations by (time-dependent) density functional theory. (C) 2013 Elsevier B.V. All rights reserved.