Sensitive detection of metastable NO and \ce{N2} by reactive collisions with laser-excited Li

Abstract

In a proof-of-principle experiment, we demonstrate that metastable nitric oxide molecules, NO(a${}^4{\Pi }_i$), generated inside a pulsed, supersonic beam, can be detected by reactive gas-phase collisions with electronically excited Li atoms in the $2^2$P${}_{3/2}$ state. Since the internal energy of NO(a${}^4{\Pi }_i$, $v\le 4$) is lower than the ionization potential of Li in the $2^2$S${}_{1/2}$ electronic ground state, we observe that the product ion yield arising from autoionizing NO(a${}^4{\Pi }_i$)+Li($2^2$S${}_{1/2}$) collisions is a factor of 21 lower than the ion yield from NO(a${}^4{\Pi }_i$)+Li($2^2$P${}_{3/2}$) collisions. We also compare our findings with measurements of relative rates for collisions of metastable \ce{N2}+Li($2^2$S${}_{1/2}$) and metastable \ce{N2}+Li($2^2$P${}_{3/2}$) reactive collisions. Using this detection method, we infer densities of $\approx 600$ NO(a${}^4{\Pi }_i$) molecules/cm${}^3$ and $\approx 6\cdot 10^4$ metastable \ce{N2} molecules/cm${}^3$ in the interaction region. Our results also allow for an estimate of the fractional population of NO(a${}^4{\Pi }_i$, $v\ge 5$) prior to the collision process. The production of NO(a${}^4{\Pi }_i$) in selected vibrational states using laser excitation from the X${}^2{\Pi }_r$ ground state will open possibilities for the detailed study of vibrational-state-selected NO(a${}^4{\Pi }_i$)-Li($2^2$P${}_{3/2}$) collisions.

14 pages, 3 figures

References in corpus (3)

• Observation of Quantum Effects in sub Kelvin Cold Reactions
• The radiative lifetime of metastable CO ($a^3\Pi ,v=0$)
• Energy dependent stereodynamics of the Ne(${}^3$P${}_2$)+Ar reaction