Pump–probe lifetime measurements on singlet ungerade states in molecular nitrogen

Excited-state lifetimes for a number of vibronic states of 1Πu symmetry in molecular nitrogen have been determined experimentally in a laser-based pump–probe scheme using a coherent and tunable extreme ultraviolet source based on harmonic generation. States investigated in 14N2 were b 1Πu(v=6–9), of valence character, and c3 1Πu(v=1) and o3 1Πu(v=1), of Rydberg character. In the case of b 1Πu(v=7) and c3 1Πu(v=1), rotationally dependent predissociation was observed. States studied in 15N2 were b 1Πu(v=5) and c3 1Πu(v=1); in addition, lifetimes of the c′4 1Σu+(v=0,1) and b′ 1Σu+(v=1) states were determined. The lifetimes show a dependence on the vibrational quantum number and isotope.