C6- electronic relaxation dynamics probed via time-resolved photoelectron imaging

Anion time-resolved photoelectron imaging has been used to investigate the electronic relaxation dynamics of C-6(-) following excitation of the (C) over tilde (2)Pi(g)<--(X) over tilde (2)Pi(u) and 2 (2)Pi(g)<--(X) over tilde (2)Pi(u) 0(0)(0) transitions at 607 and 498 nm, respectively. Analysis of evolving photodetachment energy distributions reveals differing relaxation pathways from these prepared states. Specifically, the (C) over tilde (2)Pi(g) 0(0) level relaxes on a time scale of 620+/-30 fs to vibrationally hot (similar to2.0 eV) anion ground state both directly and indirectly through vibrationally excited levels of the intermediate-lying (A) over tilde (2)Sigma(g)(+) state that decay with a time scale of 2300+/-200 fs. In contrast, the 2 (2)Pi(g) 0(0) level relaxes much more quickly (<100 fs) to vibrationally hot (similar to2.5 eV) anion ground state directly and with transient population accumulation in the (A) over tilde (2)Sigma(g)(+), (B) over tilde (2)Sigma(u)(+), and C (2)Pi(g) electronic levels, as determined by spectral and time-scale analyses. This work also presents the experimental observation of the optically inaccessible (B) over tilde (2)Sigma(u)(+) state, which is found to have an electronic term value of 1.41+/-0.05 eV. (C) 2004 American Institute of Physics.