Photoelectron spectroscopy of HNO− and DNO−

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Abstract
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 à 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.