50.94 amu

dimer vibrational frequency = 536.9 $cm-1$

dimer force constant = 4.33 mdyne/Å

References

"Raman Spectra of Mass-Selected Vanadium Dimers in Argon Matrices"

Zhendong Hu, Bo Shen, Qinwei Zhou, S. Deosaran, D.M. Lindsay and W. Harbich,

J. Chem. Phys. 95, 2206 (1991).