Optical excitation in the chromium dimer cation, Cr2+, is investigated by photon-trap and photodissociation-action spectroscopy under a cryogenic condition in an ion trap. The former provides direct measurement of an absorption spectrum with high sensitivity, where cross sections as small as 0.4 Å2 at the maximum are detectable. The dissociation cross sections are thus compared with those of absorption quantitatively. The spectra in the 2.2-eV region obtained by both methods are found to be equivalent. The present results are consistent with our assignment that the excited state is repulsive, in contrast to a previous report suggesting predissociation.
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