Diatomic and triatomic scandium and diatomic manganese: A resonance Raman study

Resonance and preresonance Raman spectra of Mn and Sc containing argon matrices are reported. For scandium, we assign the progressions to the diatomic and triatomic molecules. The former is found to have vibrational constants ω″e=239.9 cm−1 and ω″ex″e=0.93 cm−1. The latter is best described as an equilateral or near equilateral triangle with a symmetric stretching vibrational frequency of 248 cm−1 and a degenerate (asymmetric stretch–bend) vibrational frequency of 150 cm−1. In addition a low lying electronic state 395 cm−1 above the ground state is attributed to Sc3 based on the observation of a second progression. In Mn containing matrices one identifies three progressions with nearly equivalent vibrational spacings and assigns them to Mn2. The ground state vibrational constants of Mn2 are found to be ω″e=124.7 cm−1 and ω″ex″e=0.24 cm−1. Two more progressions resulting from transitions to states 135.7 and 196.7 cm−1 above the ground state are interpreted by assuming Mn2 to be an antiferromagnetic dimer possessing several spin states whose energy spacings are given by the Landé interval rule. With the frequencies of Mn2 and Sc2 one now has all the frequencies of the first row transition-metal diatomics. The trends across the periodic table are discussed and the properties of diatomics are compared with those of the analogous bulk metals.