Knowledge Bank

We report the 488 nm negative ion photoelectron spectra of the first row transition metal trimers $Cr3$, $V3$ and $V2Ni$, which were prepared in a liquid nitrogen cooled flowing afterglow ion source. The photoelectron transitions to the lowest observed electronic states of $Cr3$, $V3$ and $V2Ni$, which are assumed to be their ground states, each show two active vibrational modes with frequencies ($\pm$$15cm-1$) in the neutral clusters of 465 and $135cm-1$ ($Cr3$), 470 and $205cm-1$ ($V3$), and 415 and $250cm-1$ ($V2Ni$). For the homonuclear trimers, these are assigned as the totally symmetric stretching and bending modes, respectively, of $C2$, structures. In the mixed early-late transition metal cluster $V2Ni$, the higher frequency mode may involve primarily V-V stretching and the lower one $Ni-V2$ stretching and/or bending. For all three systems, a comparison of the observed stretching frequencies to those of $Cr2$ ($452cm-1$) and ($530cm-1$), which have formal bond orders of 6 and 5, respectively, suggest that the triatomic clusters also contain multiple Cr-Cr or V-V bonds. A transition to an excited electronic state of $Cr3$ lying 2850$\pm$20 $cm1$ above its ground state is also observed, accompanied by a long vibrational progression in a (presumably bending) mode with a neutral molecule frequency of 170$\pm$15 $cm1$ in this state. The electron affinities of $Cr3$, $V3$ and $V2Ni$ are determined to be 1.389, 1.103 and 1.112 ($\pm$0.006) eV, respectively.