Laser photoelectron spectroscopy of MnH− and FeH−: Electronic structures of the metal hydrides, identification of a low-spin excited state of MnH, and evidence for a low-spin ground state of FeH

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Abstract
The laser photoelectron spectra of MnH− and MnD−, and FeH− and FeD− are reported. A qualitative description of the electronic structure of the low‐spin and high‐spin states of the metal hydrides is developed, and used to interpret the spectra. A diagonal transition in the photodetachment to the known high‐spin, 7Σ+, ground state of MnH is observed. An intense off‐diagonal transition to a state of MnH, at 1725±50 cm−1 excitation energy, is attributed to loss of an antibonding electron from MnH−, to yield a low‐spin quintet state of MnH. For FeH− the photodetachment to the ground state is an off‐diagonal transition, attributed to loss of the antibonding electron from FeH−, to yield a low‐spin quartet ground state of FeH. A diagonal transition results in an FeH state at 1945±55 cm−1; this state of FeH is assigned as the lowest‐lying high‐spin sextet state of FeH. An additional excited state of MnH and two other excited states of FeH are observed. Excitation energies for all the states are reported; vibrational frequencies and bond lengths for the ions and several states of the neutrals are also determined from the spectra. The electron affinity of MnH is found to be 0.869±0.010 eV; and the electron affinity of FeH is determined to be 0.934±0.011 eV. Spectroscopic constants for the various deuterides are also reported.