Cotton et al. reported the Raman spectrum of Cr 2 (mhp) 4 and assigned the ground state Cr-Cr stretching mode at 556 cm -1 . 11 At the time, this was the highest M-M stretching mode ever reported by a large margin and the Cr 2 (dmp) 4 complex, when measured, was expected to lead to an even higher value. This value is consistent with an empirically assigned force constant based on a simple diatomic oscillator approximation employing the measured Cr-Cr distance. However, the vibronic features in the absorption and emission spectra as well as combined infrared and Raman analysis performed by Manning and Trogler ruled out this assignment suggesting that ν(Cr 2 ) lies at a much smaller wavenumber, either 340 or 400 cm -1 . They specifically note that either of the two Raman bands could be the Cr-Cr stretching mode but could not obtain solution spectra to further solidify the assignment. Since a vibronic progression at 320 cm -1 , assigned to the so-called δ → δ * excited state, was also observed, Manning and Trogler suggested that the 340 cm -1 peak was more likely to be the Cr-Cr stretching mode. This was based on the observation of a reduction in ν(M 2 ) by 10-15% in the excited state for quadruple bonded M 2 systems.