Photoelectron spectroscopy of HNO⁻ and DNO⁻

We have obtained the photoelectron spectra of HNO⁻ and DNO⁻ using a recently constructed negative ion photoelectron spectrometer. We observe detachment to three different electronic states of HNO and DNO, namely the X̃ ¹A′, ã ³A′′, and Ã ¹A′′ states. The electron affinity of HNO is determined to be 0.338±0.015 eV while that of DNO is 0.330±0.015 eV. The ã ³A′′ state, which has not been observed directly before, is found to lie 0.778±0.020 eV above the X̃ ¹A′ state in HNO and 0.785±0.020 eV in DNO. We see vibrational excitation up to ν′₂=3 of the ν₂ (N–O stretch) mode in the HNO and DNO X̃ ¹A′ state. In the ã ³A′′ and à ¹ A′′ states, we see excitation of both ν₂ and ν₃ (H–N–O bend) modes. The fundamental frequencies for the ã ³A′′ state are ν₂ =1468±140 cm⁻¹ and ν₃=992±150 cm⁻¹ for HNO and ν₂= 1452±140 cm⁻¹ and ν₃=750±140 cm⁻¹ for DNO. Analysis of transitions from vibrationally excited ions gives a ν₂ fundamental frequency of 1153±170 cm⁻¹ in HNO⁻ and 1113±170 cm⁻¹ in DNO⁻. A study of the angular distribution of the photodetached electrons yields the values of β, the anisotropy parameter, for the various transitions in the spectrum. A Franck–Condon factor analysis of the HNO X̃ ¹A′ band results in an estimate of the N–O bond length in the negative ion of 1.33±0.02 Å.