We employ a surface hopping trajectory method to study the rapid nonadiabatic relaxation after an excess electron is injected in unperturbed fluid helium. Several distinctively different relaxation processes, characterized by their relative importance at different times during the relaxation to a localized equilibrium state are detailed. These processes include: Short time nonadiabatic leakage from cavity to cavity, exploring the fluctuating unperturbed solvent structure. This relaxation involves slow drifting of the occupied state through a continuum of levels. This is followed by rapid diabatic expansion of a particular solvent cavity once the electron–solvent forces begin to take effect on the solvent atoms in a particular region of the fluid. We also study the importance of nonadiabatic hang up trajectories in which the excess electron gets caught in the first excited state of a bistable well potential offered by a pair of closely coupled cavities in the solvent. We study the density dependence of the time scales and relative importance of these different processes and their influence on the transient absorption spectrum after electron injection into an unperturbed fluid. Though the dynamical properties of excess electrons under the conditions considered here have never been studied before, the behavior is remarkably similar to that observed in both experimental and theoretical studies of electron hydration dynamics, indicating that the processes we describe in this paper may be very general relaxation mechanisms for localization and trapping in fluids.

1.
B.
Space
and
D. F.
Coker
,
J. Chem. Phys.
94
,
1976
(
1990
).
2.
J. C.
Tully
,
J. Chem. Phys.
93
,
1061
(
1990
).
3.
D. F.
Coker
,
D.
Thirumalai
, and
B. J.
Berne
,
J. Chem. Phys.
86
,
5689
(
1987
).
4.
D. F.
Coker
and
B. J.
Berne
,
J. Chem. Phys.
89
,
2128
(
1988
).
5.
D.
Chandler
,
Y.
Singh
, and
D. M.
Richardson
,
J. Chem. Phys.
81
,
1975
(
1984
).
6.
M.
Sprik
,
M. L.
Klein
, and
D.
Chandler
,
J. Chem. Phys.
83
,
3042
(
1985
).
7.
P. J.
Rossky
and
J.
Schnitker
,
J. Phys. Chem.
92
,
4277
(
1988
).
8.
J.
Schnitker
,
K.
Motakabbir
,
P. J.
Rossky
, and
R. A.
Friesner
,
Phys. Rev. Lett.
60
,
456
(
1988
).
9.
M.
Sprik
,
R. W.
Impey
, and
M. L.
Klein
,
J. Chem. Phys.
83
,
5802
(
1985
).
10.
M.
Sprik
,
R. W.
Impey
, and
M. L.
Klein
,
J. Stat. Phys.
43
,
967
(
1986
).
11.
F. J.
Webster
,
J.
Schnitker
,
M. S.
Friedrichs
,
R. A.
Friesner
, and
P. J.
Rossky
,
Phys. Rev. Lett.
66
,
3172
(
1991
).
12.
F.
Webster
,
P. J.
Rossky
, and
R. A.
Friesner
,
Comp. Phys. Commun.
63
,
494
(
1991
).
13.
F. H.
Long
,
H.
Lu
, and
K. B.
Eisenthal
,
Phys. Rev. Lett.
64
,
1490
(
1990
).
14.
H.
Lu
,
F. H.
Long
, and
K. B.
Eisenthal
,
J. Opt. Soc. Am.
7
,
1511
(
1990
).
15.
A.
Migus
,
Y.
Gauduel
,
J. L.
Martin
, and
A.
Antonetti
,
Phys. Rev. Lett.
58
,
1559
(
1987
).
16.
Y.
Gauduel
,
S.
Pommeret
,
A.
Mingus
,
N.
Yamada
, and
A.
Antonetti
,
J. Am. Chem. Soc.
112
,
2925
(
1990
).
17.
Y. Gauduel, S. Pommeret, N. Yamada, A. Mingus, and A. Antonetti, Femtosecond dynamics of a single electron transfer in aqueous media. Ultrafast phenomena VII (1990), Monterey California.
18.
Y.
Wang
,
M. K.
Crawford
,
M. J.
McAuliffe
, and
K. B.
Eisenthal
,
Chem. Phys. Lett.
74
,
160
(
1980
).
19.
G. A.
Kenney-Wallace
and
C. D.
Jonah
,
J. Phys. Chem.
86
,
2572
(
1982
).
20.
J. C.
Tully
and
R. K.
Preston
,
J. Chem. Phys.
55
,
562
(
1971
).
21.
J. C. Tully, in Dynamics on Molecular Collisions, Part B, edited by W. H. Miller (Plenum, New York, 1976), p. 217.
22.
E. E. Nikitin, in Chemische Elementarprozesse, edited by H. Hartmann (Springer, Berlin, 1968).
23.
E. E. Nikitin and S. Ya. Umanskii, Theory of Slow Atomic Collisions (Springer, New York, 1984).
24.
P. J.
Kuntz
,
J. Chem. Phys.
95
,
141
(
1991
).
25.
P. J.
Kuntz
and
J. J.
Hogreve
,
J. Chem. Phys.
95
,
156
(
1991
).
26.
J. K. Cullum and R. A. Willoughby, Lanczos Algorithms for Large Symmetric Eigenvalue Computations (Birkhauser, Boston, 1985).
27.
N. R.
Kestner
,
J.
Jortner
,
M. H.
Cohen
, and
S. A.
Rice
,
Phys. Rev. A
140
,
56
(
1965
).
28.
B. Space, D. F. Coker, H. Liu, B. J. Berne, and G. Martyna (in preparation).
29.
The energy levels in the trajectories reported in this paper, and our previous dynamical studies all change fairly smoothly with time on the picosecond time scales for which we follow the dynamics. These variations in the energy levels are determined by fluctuations in the size of the solvent cavities which occur on this typical nuclear dynamical time scale. In the recent work of Cukier and co-workers (Ref. 30) where they study ground state adiabatic dynamics of electrons in dense fluid helium, they present ground state excess electronic energy trajectories which exhibit fluctuations on the order of 10–15 eV on a femtosecond time scale (see Fig. 6 of Ref. 30). We suggest that it is highly unlikely that the energy of an excess electron in a simple fluid, being driven by solvent fluctuations, could fluctuate on the order of magnitude of half the ionization energy of a helium atom, and on such a rapid time scale (Ref. 31).
30.
S. Y.
Sheu
and
R. I.
Cukier
,
J. Chem. Phys.
94
,
8252
(
1991
).
31.
D. F. Coker and B. J. Berne, J. Chem. Phys. (submitted as a Letter).
This content is only available via PDF.
You do not currently have access to this content.