TY - JOUR
T1 - Electronic relaxation dynamics of water cluster anions
AU - Bragg, Arthur E.
AU - Verlet, Jan R.R.
AU - Kammrath, Aster
AU - Cheshnovsky, Ori
AU - Neumark, Daniel M.
PY - 2005/11/2
Y1 - 2005/11/2
N2 - The electronic relaxation dynamics of water cluster anions, (H 2O)n-, have been studied with time-resolved photoelectron imaging. In this investigation, the excess electron was excited through the p←s transition with an ultrafast laser pulse, with subsequent electronic evolution monitored by photodetachment. All excited-state lifetimes exhibit a significant isotope effect (τD2O/τH2O ∼2). Additionally, marked dynamical differences are found for two classes of water cluster anions, isomers I and II, previously assigned as clusters with internally solvated and surface-bound electrons, respectively. Isomer I clusters with n ≥ 25 decay exclusively by internal conversion, with relaxation times that extrapolate linearly with 1/n toward an internal conversion lifetime of 50 fs in bulk water. Smaller isomer I clusters (13 ≤ n ≤ 25) decay through a combination of excited-state autodetachment and internal conversion. The relaxation of isomer II clusters shows no significant size dependence over the range of n = 60-100, with autodetachment an important decay channel following excitation of these clusters. Photoelectron angular distributions (PADs) were measured for isomer I and isomer II clusters. The large differences in dynamical trends, relaxation mechanisms, and PADs between large isomer I and isomer II clusters are consistent with their assignment to very different electron binding motifs.
AB - The electronic relaxation dynamics of water cluster anions, (H 2O)n-, have been studied with time-resolved photoelectron imaging. In this investigation, the excess electron was excited through the p←s transition with an ultrafast laser pulse, with subsequent electronic evolution monitored by photodetachment. All excited-state lifetimes exhibit a significant isotope effect (τD2O/τH2O ∼2). Additionally, marked dynamical differences are found for two classes of water cluster anions, isomers I and II, previously assigned as clusters with internally solvated and surface-bound electrons, respectively. Isomer I clusters with n ≥ 25 decay exclusively by internal conversion, with relaxation times that extrapolate linearly with 1/n toward an internal conversion lifetime of 50 fs in bulk water. Smaller isomer I clusters (13 ≤ n ≤ 25) decay through a combination of excited-state autodetachment and internal conversion. The relaxation of isomer II clusters shows no significant size dependence over the range of n = 60-100, with autodetachment an important decay channel following excitation of these clusters. Photoelectron angular distributions (PADs) were measured for isomer I and isomer II clusters. The large differences in dynamical trends, relaxation mechanisms, and PADs between large isomer I and isomer II clusters are consistent with their assignment to very different electron binding motifs.
UR - http://www.scopus.com/inward/record.url?scp=27544495469&partnerID=8YFLogxK
U2 - 10.1021/ja052811e
DO - 10.1021/ja052811e
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AN - SCOPUS:27544495469
SN - 0002-7863
VL - 127
SP - 15283
EP - 15295
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 43
ER -