Chromium trimer has been the subject of more than 30 experimental and computational studies, yet its geometric and electronic structures remain elusive. Here we describe a 488 nm anion photoelectron spectrum that displays vibrationally resolved transitions from the Cr3- ground state to several states of neutral Cr3. Assigning the lowest energy observed state of Cr3 as its ground state gives an electron affinity of 1.394 ± 0.010 eV. Progressions in two vibrational modes provide frequencies (± 20 cm-1) in Cr3 of 485 and 130 cm-1 (120 cm-1 in the anion). A transition to a Cr3 state lying 2660 ± 50 cm-1 higher in energy displays a progression in the latter mode with an increased frequency of 165 ± 20 cm-1. Franck-Condon fits to the spectra provide estimates of geometry differences among the observed states of Cr3 and Cr3-. Weaker transitions to higher energy states of Cr3 are also observed. These results suggest structures in which one Cr atom is loosely bonded to a multiply 3d-3d bonded dimer. They are discussed in light of the diverse predictions for Cr3 or its ions that incorporate these features, including acute isosceles triangular (C2v), scalene (Cs), and asymmetric linear (C∞v) structures.

Anion photoelectron spectroscopy of chromium trimer

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