The 476-514-nm photoelectron spectra of Cr2-, recorded at 4-meV resolution, show vibrationally resolved transitions to the ground state and to one excited electronic state of neutral Cr2. The measured electron affinity of Cr2 is 0.505 +/- 0.005 eV. Observed vibrational energies in the 1SIGMA(g)+ ground state of Cr2 up to upsilon = 9, 3040 cm-1 above the zero point level, fit a Morse potential with omega(e) = 480.6 +/- 0.5 cm-1 and omega(e)x(e) = 14.1 +/- 0.3 cm-1. Twenty additional Cr2 levels that are evenly spaced with a 128-cm-1 average interval are observed 4880-7320 cm-1 above the 0-0 transition. Based on the measured isotope shift for Cr-52(2) and (CrCr)-Cr-50-Cr-52 and other considerations, we assign these as highly excited vibrational levels of the Cr2 ground state. An RKR potential is reported for this state that fits all of the measured vibrational levels to within experimental error. The observed approximately 128-cm-1 intervals are similar to the 110-cm-1 intervals predicted by Goodgame and Goddard for the 4s-4s bonded outer well of a double-minimum ground-state potential. However, the observed intervals occur at much lower energies above the zero-point level than are predicted, and the fitted potential obtained here differs considerably from the MGVB potential. Intensities of transitions to v greater-than-or-equal-to 2 levels in the photoelectron spectrum do not follow a Franck-Condon intensity profile; in addition, they vary dramatically with laser wavelength. Peak spacings from the 0-0 transition, however, are not wavelength dependent. These results indicate that the intensities of these relatively weak spectral features are strongly affected by an indirect photodetachment process involving a resonant autodetaching state of the Cr2- anion, a possible assignment for which is proposed. The spectrum also shows a transition to an excited electronic state of neutral Cr2 14 240 +/- 20 cm-1 above the ground state. This excited state has a high vibrational frequency (DELTAG1/2) of 574 +/- 10 cm-1 and a short 1.65 +/- 0.02-angstrom bond length. It is assigned as a 3SIGMA(u)+ state with single occupation of the 4ssigma(g) orbital and the 4ssigma(u)* orbital. For the ground state of the Cr2- anion, we obtain DELTAG1/2 = 411 +/- 10 cm-1, omega(e) = 440 +/- 20 cm-1, omega(e)x(e) = 14 +/- 6 cm-1, r(e) = 1.705 +/- 0.010 angstrom, and a bond dissociation energy 0.17 +/- 0.01 eV lower than that of Cr2. The anion ground state is assigned as a 2SIGMA(u)+ state in which the extra electron occupies the 4ssigma(u)* orbital.
