Femtochemistry of mass-selected negative-ion clusters of dioxygen: Charge-transfer and solvation dynamics

Abstract

Femtosecond, time-resolved photoelectron spectroscopy is used to investigate the dissociation dynamics of mass-selected anionic molecular-oxygen clusters. The observed transient photoelectron signal for the clusters (O2)n− (n=3–5) shows the O2− production; for n=1 and 2, we observe no time-dependence at this wavelength of 800 nm. The observed transients are bi-exponential in form with two distinct time constants, but with clear trends, for all investigated cluster sizes. These striking observations describe the reaction pathways of the solvated core and we elucidate two primary processes: Charge transfer with concomitant nuclear motion, and direct dissociation of the O4− core-ion via electron recombination; the former takes 700–2700 fs, while the latter is on a shorter time scale, 110–420 fs. Both rates decrease differently upon increasing cluster size, indicating the critical role of step-wise solvation.

Ultrafast vectorial and scalar dynamics of ionic clusters: Azobenzene solvated by oxygen

“…8,9,13 Here, h is the 800 nm pump photon energy, A ·O 2 − and A ·O 4 − · ͑O 2 ͒ n−2 are the charge-transfer complexes, and ER and D denote electron recombination and dissociation, respectively. As discussed earlier in Sec.…”

“…13,9 Briefly, negatively charged A m − ͑O 2 ͒ n clusters were generated by crossing a 1.0 keV electron beam with a supersonic expansion of azobenzene/oxygen mixtures. The azobenzene/O 2 gas mixture was prepared by passing the oxygen gas ͑400 kPa͒ through a sample oven containing azobenzene ͑Aldrich, 98%͒ vapor at 100°C.…”

Femtosecond dynamics of solvated oxygen anions. I. Bifurcated electron transfer dynamics probed by photoelectron spectroscopy

“…In an earlier communication, 9 we reported on studies of O 2 Ϫ clusters, and in this paper we give a full account of the study and extend the scope to include clusters of O 6 Ϫ with a variety of solvents, XϭO 2 , N 2 , Xe, or N 2 O. Specifically, we report on the femtosecond ͑fs͒ time-resolved photoelectron ͑PE͒ spectra.…”

“…Second, upon irradiation with a 800 nm fs pulse, the electron migrates from the O 4 Ϫ core to the neutral O 2 molecule; subsequently, an O 2 Ϫ fragment is generated via two different channels, as discussed in Ref. 9. The solvent, N 2 , Xe, or N 2 O is weakly bound to the O 4 Ϫ core and not directly involved in an electron migration process, as evidenced from the photoelectron spectra and the nascent fragments produced.…”

“…These microscopic solvation processes, which may involve energy redistribution, electron transfer, and vibrational predissociation, have been examined in a variety of ionic [1][2][3][4][5][6][7][8][9] and neutral [10][11][12][13][14] clusters.…”