Knowledge Bank

A tunable pulsed dye laser has been used to selectively excite vibrational levels of the A$ ^{2}\pi_{u}$ state of $N2+$. The collisional deactivation processes for these levels have been deduced from their laser induced fluorescence. An optical-optical double resonance experiment using a second laser confirms that the ions originally pumped into the $A2\pi u$ state are rapidly deactivated by collisions with He into high vibrational levels of the ground X$ ^{2}\pi_{g}^{+}$ state. Time resolved studies show that the population of a given high vibrational level of the $X2\Sigma g+$ state returns into lower A$ ^{2}\pi_{u}$ state levels giving rise to vibrational relaxation within the A state. In homonuclear $N2+$, where g--u symmetry considerations prohibit X and A state perturbations, these processes proceed as rapidly as in heteronuclear species where perturbations are known to be present in the free molecule.