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

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.