Mass selected anion-zero kinetic energy photoelectron spectroscopy (anion-ZEKE): Ground and low excited states of FeO

Photodetachment-photoelectron (PD-PES) and anion-zero kinetic energy photoelectron (anion-ZEKE) spectra of FeO have been measured. The vibrational progression bands of the X ⁵Δ_i(FeO)←X ⁵Δ_7/2(FeO^-) transition in the PD-PES spectrum exhibit substructure which could not be resolved in earlier PD-PES spectra. A comparison with the high resolution anion-ZEKE spectrum clearly shows the existence of a second low energetic electronic state which could be the a ⁷Σ⁺ of neutral FeO proposed by several authors. In addition, for the A ⁵Σ⁺ state of FeO an excess energy of 4050 cm^-1 was found. Vibrational frequencies for the X ⁵Δ, a ⁷Σ⁺ , and A ⁵Σ⁺ states have been determined as 882, 887, and 800cm^-1. All spin orbit splittings of the neutral and anionic ground states could be measured directly or deduced from spin orbit combination transitions. We succeeded in resolving the rotational envelope of the vibrational origin of the neutral-anion ground states transition with indicated single rotational lines of the ΔJ = +3/2 branch.