Quantum-state-resolved 2-level femtosecond rotational coherence spectroscopy: Determination of rotational constants at medium and high J in Li2, a simple diatomic system

A series of rotational wave packet recurrences originating from single 2-level coherent rotational superpositions are observed in the E(1Σg+) state of Li2. The rotational wave packet is created by ultrafast laser excitation from a specific ro-vibrational level in the A(1Σu+) state selected by cw laser excitation. Using this technique the rotational constant and the centrifugal distortion constant are determined for high J levels of the ν = 9 vibrational level in the E(1Σg+) state. This technique is discussed vis-à-vis traditional forms of ultrafast rotational coherence spectroscopy where information primarily at low J is obtained.