Title

All-optical triple resonance spectroscopy of Na2 and scheme for state-selective formation of highly rotationally-excited diatomic molecules

Date of Completion

January 2000

Keywords

Physics, Molecular|Physics, Atomic|Physics, Optics

Degree

Ph.D.

Abstract

This investigation focuses on the spectroscopic study of the fundamental question: “how to control and manipulate molecules”. The following three studies touch these questions from different angles. ^ First in Chapter 2, we use the powerful AOTR to probe Na2 molecules near their equilibrium intemuclear distance, Re(∼3Å), but at high levels of electronic excitation. For the nf(l = 3) series of Na2, quantum defects are calculated from theoretical values of the core quadrupole moment and polarizabilities. We predict the stroboscopic effect should first occur when n = 52 for the nf series, as we observe, rather than at n = 69 for the np series. Our data thus confirm that the strongest series is the nf. Hence the ionization potential is not 39478.75 ± 0.04 cm−1 as previously reported, but rather 39478.101 ± 0.013 cm−1, implying a molecular ion dissociation energy of D00(Na 2+) = 7914.038 ± 0.014 cm−1. ^ Then in Chapter 3, we again use AOTR to shift the distance probed to ∼6.44Å, but again explore high levels of electronic excitation. We have observed the 51Πu, 61Σu + and 71Σu+ states of Na2. Although the absolute vibrational numbering is uncertain, the rotational constants are obtained. The Franck-Condon window concept is presented with calculated Franck-Condon factors based on the theoretical 5 1Πu, 61Σu+ and 71Σu+ potential energy curves of Magnier. Finally in Chapter 4, the molecules again remain at relatively short distance near Re, but a scheme is proposed for making highly rotationally excited diatomic molecules (“Super Rotors”) in their ground vibrational and electronic state, e.g. 6Li 2 X 1Σg+ (v = 0, J ≥ 115) where the rotational energy exceeds the bond strength (E(0,J)-E(0,0) ≥ D00). Such levels, while strictly speaking quasibound, have very long tunneling lifetimes, and should have very interesting and unique collisional properties, especially at low temperature. The rotation of the molecules is “spun up” by sequential irradiation by R branch photons in the A 1Σu+–X 1Σg+ bands starting with cold molecules at low J. Spontaneous emission to other vibrational levels is overcome by using a pump laser and its multiple Raman sidebands as in previous work on “spinning down” diatomics. ^