Reduction of 1+1 REMPI spectra to population distributions: Saturation and intermediate state alignment effects

A two‐step methodology is presented for extracting ground state population distributions from 1+1 resonance enhanced multiphoton ionization (REMPI) spectra. In the first step the ion signal is corrected for variation with laser intensity as it is collected, generating an iso‐power spectrum. In the second step populations and alignments are derived from the iso‐power spectrum by correcting for the interdependent effects of saturation and intermediate state alignment. This procedure is applied to a room temperature thermal distribution of nitric oxide using the 1+1 REMPI process in which lines of the NO A 2Σ+–X 2Π (0, 0) band constitute the resonant transition. The present treatment is able to recover the known rovibrational population distribution, independent of branch choice, over a wide range of practical operating conditions.