Single-photon threshold photoionization of NO

Single‐photon threshold photoionization spectra for jet‐cooled NO have been measured for the v^+=0 and 1 vibrational levels of the X ^1Σ^+ ground state of NO^+. The NO^+ rotational state distribution for the v^+=0 level is shown to be perturbed by nearby autoionizing levels, whereas the v^+=1 level exhibits a cation rotational distribution which is in near quantitative agreement with calculated spectra near threshold. Only small changes in total angular momentum are observed (‖ΔJ‖=‖J^+ − J‘‖≤5/2) even though a wide range of photoelectron angular momenta (l=0–3) are predicted to contribute to the near‐threshold photoelectron continua. The present results are also discussed in light of recently published two‐photon threshold photoionization spectra of NO which exhibit nearly identical NO^+ rotational state distributions.