One-photon mass-analyzed threshold ionization spectroscopy of bis (η6-benzene)chromium and its benzene and Ar clusters

The one-photon mass-analyzed threshold ionization (MATI) spectroscopy of bis(eta(6)-benzene)chromium is reported. The adiabatic ionization energy is accurately measured to be 44 087 +/- 5 cm(-1) (5.4661 +/- 0.0006 eV). The Cr-benzene stretching vibrational mode in the ion with a fundamental frequency of 264 cm-1 is found to be optically active. The MATI spectra of bis(eta(6)-benzene)chromium.Ar and bis(eta(6)-benzene)chromiumbenzene clusters are also reported to give ionization potentials of 43 941 +/- 5 cm(-1) (5.4480 +/- 0.0006 eV) and 42 576 +/- 5 cm(-1) (5.2788 +/- 0.0006 eV), respectively. A van der Waals mode with the fundamental frequency of 65 cm(-1) is optically active in the MATI spectrum of the bis(eta(6)-benzene)chromium-benzene cluster, suggesting an intermolecular structural change upon ionization. The larger bis(eta(6)-benzene)chromium(benzene)(n) (n = 2-9) clusters are found to be generated in the molecular beam. Their ionization potentials, from photoionization efficiency spectra, show the gradual decrease as the cluster size gets larger, down to the value of 5.02 eV for n = 9.