Predissociative linewidths of (4pσ) M 2Σ+ (v=1) and (3dσ,π) H 2Σ+, H′ 2Π (v=2) Rydberg states of NO studied by the two-color laser-induced grating technique

Abstract

The two-color laser-induced grating (TC-LIG) technique has been employed to probe the predissociative Rydberg states (4pσ) M 2Σ+ (v=1) and (3dσ,π) H 2Σ+, H′ 2Π± (v=2) and the non-Rydberg B 2Π (v=26) state of nitric oxide. The ultraviolet pump laser frequency is fixed to a specific rotational line of the A 2Σ+ (v′=1 and 2)←X 2Π3/2 (v″=0) transition of NO. Interference of two pump laser beams crossing at a small angle in the gas sample forms a population grating. Then, the visible probe laser beam is diffracted off the grating as the signal beam when the probe laser frequency is resonant to a transition from the rotational level excited by the pump laser. Term values and rotational assignments of the H 2Σ+, H′ 2Π± (v=2)–B 2Π3/2 (v=26) states have been established for the first time, resulting in the value of ∼1.77 cm−1 for the l-uncoupling constant. Line broadenings due to predissociation are observed in the TC-LIG spectra for the M 2Σ+ (v=1) and H 2Σ+, H′ 2Π+ (v=2) states. The linewidths of the M 2Σ+ (v=1) state show no marked rotational dependence except for the N=4 level which is locally perturbed. On the other hand, the predissociative lifetimes of the H 2Σ+ and H′ 2Π+ (v=2) states exhibit a significant rotational dependence: The linewidth of the former state decreases with N, while the reverse tendency is seen for the latter. The mixing between the H 2Σ+ and H′ 2Π+ states caused by l-uncoupling explains the observed rotational dependence successfully.