ivan janeček, daniel hrivňák, and rené kalus department of physics, university of ostrava,...
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Fragmentation Dynamics of Singly Ionised Homogeneous Rare Gas Trimers from Adiabatic States
Ivan JaneIvan Janeček ,ček , Daniel HrivňákDaniel Hrivňák, , and René Kalusand René Kalus
Department of Physics, UDepartment of Physics, University of Ostrava,niversity of Ostrava,Ostrava, Czech RepublicOstrava, Czech Republic
Supported by the Grant Agency of the Czech Republic (Supported by the Grant Agency of the Czech Republic (ggrant. no. 203/02/1204)rant. no. 203/02/1204)
THEORY: Hemiquantal dynamics and extended DIM method
Neutral diatoms: empirical data Ar2 – R. A. Aziz, J. Chem. Phys. 99 (1993), 4518.Singly charged diatoms: computed ab initio by I. Paidarová and F. X. Gadéa (1996)The spin-orbit constant used is of empirical origin.
Simulation: Fragmentation of the Rg3+ cluster after sudden ionisation from energy level Ei.
++3 2 +Rg Rg Rg3 3 eRg Rg
DIM ab a1 1
ˆ ˆ ˆ( 2)n n n
a b a a
H H n H
A neutral trimer in the static equilibrium configuration (equilateral triangle) is vibrationallyexcited .
*3 3Rg Rg
E01 E03 E05 E07 E09 E11 E11 E13 E15 E17 E170
500
1000
1500
2000
Xe+ 3 Model:
DIM+SO+ID-IDHeating: DL
Xe3 3Xe
Dec
ay N
um
ber
Initial Energy level
3Xe
E01 E03 E05 E07 E09 E11 E11 E13 E15 E17 E170
10000
20000
30000
40000
50000
60000
Xe3
3Xe3Xe
Mea
n D
ecay
Tim
e
Initial Energy level
E01 E03 E05 E07 E09 E11 E11 E13 E15 E17 E17
0,00
0,25
0,50
0,75
1,00
(Xe2+Xe)+
(3Xe)+
Xe+3
Xe3
3Xe3Xe
Mea
n E
vap
ora
ted
Ch
arg
e
Initial Energy level
Xe+3
E01 E03 E05 E07 E09 E11 E11 E13 E15 E17 E170,000
0,025
0,050
0,075
0,100
Xe3
3Xe3Xe
Mea
n K
inet
ic E
ner
gy
of
Eva
po
rate
d A
tom
[eV
]
Initial Energy level
1000 10000 100000
0,00000
0,00005
0,00010
0,00015
0,00020
0,00025
0,00030
0,00035
0,00040
0,00045
0,00050
0,00055
0,00060
0,00065
Xe+
3 - Model:
DIM+SO+ID-IDHeating: DL
No
rma
lise
d C
ou
nt
Decay Time [fs]
E01 E03 E05 E07 E09 E11
channel 3 E13 E17
Now, the trimer is suddenly ionised to energy level Ei from the cation trimer energy spectrum.
After MC equilibration the heated cluster has a random configuration different from the initial one(a distorted triangle).
The molecular dynamics runs up to 105 fs.
As soon as a cluster decay is indicated,the calculations is stopped.
PRAHA
OSTRAVA
Model: DIM + SO + ID-ID*
The initial state of the neutral cluster: equilibrium geometry, zero angular momentum, nonzero vibrational kinetic energy Ek. The initial state of the ion cluster: energy level Ei, where i = 1, 3, 5, 7, 9, 11, 13, 15, 17 (double degeneration).
* From diabatic decay simulations we know that the spin orbit coupling has major influence on the time of decay, wherefore DIM model with the inclusion of the SO coupling is used, ID-ID interaction does not seem to be relevant in this case.
Results: Fragmentation of Xe3+ cluster after sudden ionisation
Field of study: Rare gas cation trimers of Ar, Kr, Xe (= Rg) with initial kinetic energy Ek from the zero point vibration energy E0
to the dissociation limit (DL) energy Edl (dissociation of the Rg3 to Rg2 and Rg). At present trimers Rg3
+ are studied. However, fragmentation of larger Rgn+ clusters (n>3) can also be computed.
0 1 2 3 4 5 6 7 8 9 10 11 12
-1,4
-1,2
-1,0
-0,8
-0,6
-0,4
-0,2
0,0
-0,4
-0,2
0,0
0,2
0,4
0,6
0,8
1,0
En
erg
y [e
V]
Y3, X3=0 [ angstrem]
E01 E03 E05 E07 E09 E11
Init. Conf.
E13 E15 E17
We have computed 2000 trajectories for each energy level. For initial heating with Ek = E0 = 0.0038 eV we have observed no decay from either energy level up to time 100 ps. In the left figure the histogram (in form of the point graph) of the time of decay is plotted for Ek = Edl = 0.0487 eV. The y-scale is correct for basic energy level only. Curves for higher adiabatic levels are shifted along the vertical axis. The main way of the decay is a fragmentation to a dimer and a single atom. One can observe quick decay from the ground state and also from E11 level, where also the fragmentation to single atoms is observed (channel 3). On the other hand, no decay has been observed for E15 level. In the right picture one can see summary of some mean values .
Bottom contour plots show the potential energy surfaces of Xe3+ for levels E11 (left) and E15 (right) as a function of xy-coordinates of the third atom Xe for fixed positions
of the two remaining atoms (1 and 2). Their distance R12 = 4.45 angstrem, which is a mean value of the shortest side of Xe3 triangle after the equilibration phase. Small points correspond to Xe3
+ configurations obtained after this phase (These configurations are initial configuration for molecular dynamics on ion cluster). The red line is an approximate “lower boundary” of the configurations. Atoms 1 and 2 are situated on axis x and have equivalent distance from axis y. Coloured circles at axes show positions of the atoms in configuration corresponding to the potential energy surface minimum (PES E11- equilateral triangle, PES E15 – equilateral triangle and linear trimer). In the case of the initial adiabatic state E15 no decay has been observed for any initial configurations, in the case of the initial adiabatic state E11, on the contrary, a frequent fragmentation has been observed, the green points relate to the initial configuration without decay observed. For illustration, sections for x 3 = 0 are plotted for all the levels in the middle graph.
Hemiquantal, mean-field dynamics (HWD) [1] and recently developed extended diatomics-in-molecules (DIM) [2, 3] models of intra-cluster interactions with the inclusion of the spin-orbit coupling (DIM +SO) [4] and the most important three-body forces induced dipole – induced dipole interactions (DIM +SO + ID-ID) [5] are used to study fragmentation of argon, krypton and xenon trimer cations after a sudden ionization of respective vibrationally excited neutral trimers.
[1] M. Amarouche, F. X.Gadea, J. Durup, Chem. Phys. 130 (1989) 145-157 [2] F. O. Ellison, J. Am. Chem. Soc. 85 (1963), 3540.[3] P. J. Kuntz & J. Valldorf, Z. Phys. D (1987), 8, 195.[4] J. S. Cohen and B. Schneider, J. Chem. Phys. 64 (1974) 3230[5] M. Amarouche et al., J. Chem. Phys. 88 (1988) 1010].
0,62
0,48 0,380,28
-0,16
-0,22-0,24
-0,26
-0,28
-0,30
-0,32
-0,34
-0,36
-0,38-0,40
-0,42 -0,44
-0,46
-0,46
-0,47-0,48
0 2 4 6 8 100
2
4
6
8
10 Y3 Y3 B Ymin
Y3 [
an
gs
tre
m]
X3 [angstrem]
Xe+
3 E
11
DIM + SO + ID-IDE
k= E
dl
<R12
> = 4.45 angstrem
Minimum energyconfiguration
0,960,94
0,92
0,900,88
0,86
0,84
0,82 0,800,78 0,760,76
0,78
0,80
0,82
0,74
0,74
0 2 4 6 8 100
2
4
6
8
10
Minimum energyconfiguration
Xe+
3 E
15
DIM + SO + ID-IDE
k= E
dl
<R12
> = 4.45 angstrem
Y3 B B Ymin
Y3 [
an
gs
tre
m]
X3 [angstrem]