A photoionization and photoelectron study of vibrational and electronic cooling in metal molecular beams

Threshold photoionization and pulsed-field-ionization zero-electron-kinetic-energy photoelectron spectra have been used to study the vibrational cooling of Cu–N(CH3)3 and the electronic cooling of Al–NH3 in helium and argon supersonic jets. The vibrational temperatures of Cu–N(CH3)3 are estimated to be ∼40 K in argon and ∼120 K in helium, whereas the electronic temperatures of Al–NH3 are about 20 and 80 K, respectively. Argon more efficiently cools the internal degrees of freedom of the metal systems, but helium provides additional spectroscopic information about the neutral molecules. The differences in the observed spectra have greatly facilitated spectral assignments for these complexes.