Higher resolution photoionization study of NO near the threshold

Abstract

The photoionization efficiency curve for NO⁺ has been obtained at a resolution of 0.14 Å (FWHM) in the region 1189–1340 Å using the molecular beam method. The observed autoionization peaks can be satisfactorily correlated with the positions of the Rydberg levels (ns, npσ, npπ, ndσ, ndπ, ndδ, and nf) observed or calculated with the quantum defects deduced from previous absorption experiments. The analysis of the autoionization structure suggests that autoionization via Δv=−1 processess are not strongly favored in comparison to Δv<−1 processes in NO. The degree of relaxation of NO (²Π_3/2) in a supersonic expansion has also been examined by comparing the relative intensity of the autoionization structure at different nozzle temperatures. A small step at 1341.5 Å which is approximately 124 cm⁻¹ lower in energy that the first onset at at 1339.32 Å is attributed to the threshold for the NO (X ² Σ⁺ v=0) ← NO (X ²Π_3/2 v=0) transition. This observation is in agreement with the previous finding that the relaxation from ²Π_3/2 to ²Π_1/2 in a free jet expansion is efficient.