Resonantly enhanced multiphoton ionization of pyrrole, N-methyl pyrrole, and furan

The resonantly enhanced multiphoton ionization (REMPI) spectra of pyrrole (C4H5N), N-methyl pyrrole (C5H7N), and furan (C4H4O) have been measured in the wavelength region from 365 to 680 nm. New and previously observed Rydberg states are reported for pyrrole and furan. Vibrational constants are presented for most of the Rydberg series. Accurate ionization potentials are derived for pyrrole (8.207 +- 0.003 eV) and N-methyl pyrrole (7.94 +- 0.02 eV). A strong two photon allowed transition is observed in N-methyl pyrrole at 41 193 cm-1 (0,0) and is attributed to an 1A2 state. The corresponding state is not seen in pyrrole; however, it may be obscured by overlapping Rydberg series. Mass spectra following REMPI for benzene, pyrrole, and furan are reported. The degree of ionic fragmentation depends upon laser power density and wavelength