Knowledge Bank

We have used pulsed laser photoionization of dry atmospheric air for the analysis of the O$2$(X$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Sigma$$\to$C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$) excitation spectrum and improved characterization of the O$2$(C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$) Ryberg state. This $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$ Ryberg state is generally very diffuse due to predissociation, but using this method, reasonable resolution in the rotational structure of the v=2 level was achieved. A simulated O$2$(X$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Sigma$$\to$C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$) excitation spectrum was calculated for line position, intensity, and linewidth that agreed very well with the experiment, providing values for $\nu$$0$, B, and D for the F1, F2, and F3 subbands of O$2$(C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$, v=2). The photoionization technique involved a combination of resonant-enhanced multi-photon ionization (REMPI), collisional excitation, and laser-induced fluorescence. A focused, ultraviolet laser pulse was used to excite the O$2$(X$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Sigma$$\to$C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$) resonant transition. The near coincident energy between the O$2$(C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$, v=2) state and the N$2$(a$\Sigma$, v=1) state resulted in rapid collisional transfer of energy to the N$2$(a) state. The N$2$(a) molecules were then photoionized by the same laser pulse to the N$2$$\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$(B) state, producing an easily observable fluorescence at 391 nm. By scanning the laser wavelength while observing the 391 nm fluoresence, details of the O$2$(C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$$\Pi$) Ryberg state could be studied.