Vibrational Spectroscopy and Structural Analysis of V+(C2H6) n Clusters (n=1-4)

The vibrational structure and binding motifs of vanadiumcation-ethaneclusters, V+(C2H6)( n ), for n = 1-4 are probed using infraredphotodissociation spectroscopy in the C-H stretching region(2550-3100 cm(-1)). Comparison of spectra toscaled harmonic frequency spectra obtained using density functionaltheory suggests that ethane exhibits two primary binding motifs wheninteracting with the vanadium cation: an end-on eta(2) configuration and a side-on configuration. Determining the denticityof the side on isomer is complicated by the rotational motion of ethane,implying that structural analysis based solely on Born-Oppenheimerpotential energy surface minimizations is insufficient and that amore sophisticated vibrationally adiabatic approach is necessary tointerpret spectra. The lower-energy side-on configuration predominatesin smaller clusters, but the end-on configuration becomes importantfor larger clusters as it helps to maintain a roughly square-planargeometry about the central vanadium. Proximate C-H bonds exhibitelongation and large red-shifts when compared to bare ethane, particularlyin the case of the side-on isomer, demonstrating initial effects ofC-H bond activation, which are underestimated by scaled harmonicfrequency calculations. Tagging several of the clusters with argonand nitrogen results in nontrivial effects. The high binding energyof N-2 can lead to the displacement of ethane from a side-onconfiguration into an end-on configuration. The presence of eitherone or two Ar or N-2 can impact the overall symmetry ofthe cluster, which can alter the potential energy surface for ethanerotation in the side-on isomer and may affect the accessibility oflow-lying electronic excited states of V+.