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 ¹∑⁺ 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.