Non-Radiative Deactivation\nin Isolated Quinoline

The photophysics\nof the S<sub>2</sub> <sup>1</sup>(ππ*)\nstate of the polycyclic aromatic nitrogen-containing hydrocarbon (PANH)\nquinoline is investigated in a free jet using a picosecond laser system.\nA [1 + 1] multiphoton ionization spectrum yields the S<sub>2</sub> origin at around 32 200 cm<sup>–1</sup> and reveals\nseveral vibronic bands. In time-resolved experiments, quinoline is\nthen excited between 312.2 and 279.7 nm. Probe wavelengths of 351\nand 263.5 nm are employed. The dynamics is monitored by time-resolved\nphotoelectron imaging. The images reveal a short-lived band at high\nelectron kinetic energies with a ps lifetime and a band at lower electron\nkinetic energies that shows an offset at long delay times. In comparison\nwith previous work, the offset is assigned to ionization from the\nT<sub>1</sub> state. Lifetimes decrease from 45 ps at the S<sub>2</sub> origin to 11 ps at +3550 cm<sup>–1</sup>. Most likely, the\nS<sub>2</sub> <sup>1</sup>(ππ*) state deactivates by internal\nconversion to the S<sub>1</sub> <sup>1</sup>(nπ*) state, followed\nby intersystem crossing to the triplet manifold.