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II. Multi photon excitation / ionization processes. Why multiphoton exitations(?); advantages/disadvantages One color experiments / data Experimental methods: Multiphoton ionization (MPI & REMPI) Data interpretations / theory: “What to see and what not to see(?)” Results / examples:
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II. Multi photon excitation / ionization processes
Simulation:
i(3D2) < X(1S+)
(0,0)
Simulation:
Be´/ Bf´ = 7.975/7.969 ±0.030cm1
De´/Df´= (0.55/0.50 ± 0.10)x103 cm1
n0 = 78625 ± 2 cm1
E´(J) = B´J(J+1) – D´J2(J+1)2
n0 = E´(v´=0) – E´´(v´´=0)
for
i(3D2) < X(1S+)
(0,0)
Fig. 2
(2+1) REMPI spectra of I2:
I2; [2P1/2]c6s;1g << X 0g
(v1,v0)
DOP
Fig. 3
I2; [2P1/2]c6s;1g << X 0g
(2+1) REMPI spectra of I2:
as well as
Rotational line series:
O: J2 < J; P: J1 < J
Q: J < J
R: J+1 < J; S: J+2 < J
Exp.
Calc.
(v1,v0) =
Dn / cm1
AB+ + e
:
AB**
i4>
i3>
Properties of AB* and AB:
 energy configurations
 molecular geometries
i2>
i1>
AB
i.e.:
II. Multi photon excitation / ionization processes
HBr:
Total angular
momentum changes
For W´=0 W ´´=0:
J3;N
J2;O
J1;P
J:Q
J+1;R
J+2;S
J+3;T
DJ = ±1
DJ = ±1
DJ = ±1
J
z
= 0
DJ = ±1,.. ,±n; n = odd; DW = 0
DJ = 0 ,±2,.. ,±n; n = even DW = 0
HBr:
II. Multi photon excitation / ionization processes
B´= 8.39±0.05 cm1
D´= (0.85±0.10)x103cm1
n0 = 82837±3 cm1
W´=3(F)
W´=2(D)
W´=1(P)
W´=0(S)
2xhn
3xhn
3xhn
½i >
1xhn
2xhn
3xhn
“New” state: L1F3 (n0 = 82837±3 cm1)
W´´=0(S)
“New” state, not detected before:
Predicted state ((s2p3)5dd)
in this region: L1F3 (n0 = ?????)
II. Multi photon excitation / ionization processes
Complicated spectra, analyses / Example I:
HCl, (3+1) REMPI:
n
cm1
3 x (1/l=333 nm)
n
cm1
Find “difference spectra” / “exp. – Calc.”
HCl, (3+1) REMPI / Simulation:
???!!
???!!
???!!
OK
OK
“Difference spectra(1)” / “exp. – Calc.”:
exp.

calc.
3 x (1/l=333 nm)
HCl, (3+1)
REMPI
exp. – calc./
“Diff.sp.(1)”
n
cm1
Difference spectra(2) = “exp. – diff. spectra(1)” / Simulation:
“Difference spectra “(1) / Simulation:
Complicated spectra, analyses / Example II:
(2,0) band
NO
z
z
W= 3/2
W= 1/2
1
z
Spinrot.
interaction
D 2S:
Orbitrot.
interaction
X 2P:
Spinorbit
interaction
(1,1)
(1,2)
(2,1)
(2,2)
E1´
E2´
2S
Spinrot.
interaction
Cv´
2P3/2
Orbitrot.
interaction
2P1/2
Av´´=0
Cv´´=0
E1´´
E2´´
2S
(11)
(22)
(12)
(21)
2P
, T=298K
(2,0)
(2,0)
(2,0)
II. Multi photon excitation / ionization processes
AB#/A#+B#
State interactions/
AB** <>AB#
&
dissociation processes
AB** > A# + B#
?
AB+ + e
AB**
:
i4>
i3>
i2>
i1>
AB
HCl; (3+1)REMPI
j3S0 < X1S+
(0,0)
?
j3S0 < X1S+
(0,0)
(3+1)REMPI
?
Comparison of (2+1) og (3+1)REMPI:
?
State interaction / perturbation j <>V(1S+) / interaction strength
explanation:
8
7
v´=24
(3+1)REMPI
Rotational perturbation
observed in vibrational
band due to the transition
I2; [2P3/2]c5s;1g << X 0g,
v1 = 0, v0 = 1
::
Because of state interactions:
[2P3/2]c5s;1g <> D´(2g)
II. Multi photon excitation / ionization processes
AB+ + e
:
AB**
i4>
i3>
i2>
Mechanism of nxhn absorption /
ionization; involvement of
intermediate states.
?
i1>
AB
N,T: I µm32s3
P,R: I µm12s1 + m32s3
I(N,T) / I(P,R) depend on
m12 and m32 or m12 /m32
Adjust m12 and m32
to obtain best fit:
W´´=0(S)
W´=0(S) W´´=0(S)
I µm12s1 + m32s3
HCl, E(1S+) X(1S+), (3+1)REMPI
m12 /m32 = 0.90±0.15
W´=1
(P)
W´=0
(S)
W´=0
(S)
Four
paths:
W´´=0(S)
W´´=0(S)
Major path
for HCl:
E(1S+)
X(1S+):
Paths vs m12 and m32 :
vs exp.: m12 /m32 = 0.90±0.15
II. Multi photon excitation / ionization processes
HBr
Surface science studies/ collaboration work with J.C. Polanyi, Toronto:
Na
Surface science studies/ collaboration work with J.C. Polanyi, Toronto:
Na
effect?
i.e.: 1) hn + NaBrH(s) > NaBr(s) + H(g)
detect / measure HBr by REMPI: observe kinetic energy.
Surface science studies/ collaboration work with J.C. Polanyi, Toronto:
Na
effect?
i.e.: 2) hn + NaBrH(s) > Na(s) + HBr#(g)
IREMPI
n
2 x (1/l=255nm)
3 x (1/l=382nm)
(3+1)REMPI simpler spectrum / “more convenient” wavelength
i.e.:
»straight line
25oC
(3+1)REMPI spectra
and s
useful to determine
N(J)
Line fit
Besta
beina lína
II. Multi photon excitation / ionization processes
3dpF1Su+ <<< X1Sg +
V. Blanchet et al., J. Chem. Phys., 119(7), 3751, (2003):
II. Multi photon excitation / ionization processes
AB = CdAr:
(v1,v0)
1>
A30+< X10+
v1+1
v1
v11
Energy
v0
0>
r (AB)
(v1,v0)
AB = I2:
1>
v1+1
[2P1/2]c6s;1g << X 0g
v1
v11
Energy
v0
0>
r (AB)
AB nxhn– (1>, 0> )/(v1+i,v0)
excitations:
(v1+1)
I
v1 +1
s
v1
1>
(v11)
Exp.
v1 1
(v1)
DE10
nxhn
v0
0>
Calc.
n
:
:
:
DE10
DE00
DE+10
BO approximation, etc.
i.e.:
nhn + AB > AB*
mhn + AB > AB+ + e (Ekin = 0)
V0=0
V1= 0 1 2 3 4 5
V0=0
V1= 0 1 2 3 4 5
V0=0
V1= 0 1 2 3 4 5
Example: Twocolour optical doule resonance (ODR)
ionization of I2:
I2+ + e
Energy
[I+I]* 0 g
(1+1)REMPI
1´ excitation
I2* B 3P0 u
((1´+1)+1) REMPI
r(II)
I2 X 1S+ g
I2+ + e
Energy
[I+I]* 0 g
I2* B 3P0 u
I2 X 1S+ g
r(II)
Please visit: http://www.raunvis.hi.is/~agust/
Acknowledgments:
Iceland:
:Benedikt G. Waage, MS student
Jón Matthíasson,
Oddur Ingólfsson, PhD
Kristján Matthíasson, MS student
Victor Huasheng Wang, research scientist
Ágúst Kvaran, professor
Acknowledgments:
Collaborators:
:Robert J. Donovan, Prof., Edinburgh University, UK
Timothy G. Wright, University of Sussex, UK
Lars Madsen, Aarhus, Denmark
NORFA network participants (?)