Implementation of Various Modalities of the Optical-Optical Double Resonance Techniques To Simplify the Interpretation of the Spectra of Highly Excited States of Nitric Oxide.

Abstract

We combined various modalities of the optical-optical double resonance (OODR) photoionization technique to simplify the interpretation of crowded molecular spectra. To demonstrate the effectiveness of our method, we applied it to the 64000 to 65200 cm(-1) spectral region of the molecule NO, where exist the following electronic states: B (2)Π (v = 21), D (2)Σ(+) (v = 5), F (2)Δ (v = 1), L (2)Π (v = 3), and K (2)Π (v = 0). This spectral region is complicated because (1) several electronic states are close in energy, (2) some of the rotational energy patterns are irregular, and (3) the relative intensity of the different bands varies markedly. We implemented four modalities of the OODR experimental technique that involved the combined use of two or three lasers. The individual rotational levels up to N' = 20 of the A(2)Σ(+) (v = 0) state were pumped as intermediate states by one-photon excitation from appropriate rotational levels in the X(2)Π (v = 0) ground state. Some of the schemes implemented provided information about line positions and relative band intensities, whereas the ion-dip detection scheme provided insight into the fate of the population in the different states. The term values that we derived are in good agreement with the literature ones. We rotationally resolved the spectra for the K (2)Π (v = 0) and B (2)Π (v = 21) states up to N = 20, and for the D (2)Σ(+) (v = 5) and L (2)Π (v = 3) states up to N = 8 and 7, respectively. Strangely, only in the rotational levels between N = 6 and N = 20 were we able to observe the F (2)Δ state, which is mostly mixed with the B' (2)Δ (v = 4) state and usually notated as F (2)Δ (v = 1) → B' (2)Δ (v = 4). We obtained the rotational constants for the B (2)Π1/2 (v = 21), L (2)Π3/2 (v = 3), and K (2)Π1/2 (v = 0) states, which had not been previously reported.