Mass analyzed threshold ionization spectroscopy of N-deuterium substituted indoline cation: isotope effect on the electronic transition, ionization and molecular vibration

The resonant two-photon ionization (R2PI) and mass analyzed threshold ionization (MATI) spectra of N-deuterium substituted indoline (indoline-d1) have been recorded. The origin of the S1←S0 transition and the adiabatic ionization energy (IE) are found to be 32254±1 and 58284±5 cm−1, corresponding to the isotope shifts of 38 and 15 cm−1, respectively. Comparing these data with those of N-deuterated aniline suggests that the five-membered ring is responsible for the observed blue shifts in the electronic energy and IE of indoline-d1. The present results also show that the N-deuteration can lead to a reduction in the frequencies of the characteristic C2-puckering, butterfly, ring twisting, and N-inversion vibrations of indoline.