Transcript KRb OSU 2011.pptx

Analysis of strongly perturbed
1 1P – 2 3S+ – b 3P states of the KRb molecule
J. T. Kim1, Y. Lee2, and B. Kim3
1Department
of Photonic Engineering, Chosun University.
2Department of Chemistry, Mokpo National University.
3Department of Chemistry, KAIST.
D. Wang
Department of Physics, The Chinese University of Hong Kong.
W. C. Stwalley, P. L. Gould, and E. E. Eyler
Physics Department, University of Connecticut.
Supported by the National Science Foundation, the Air Force
Office of Scientific Research, the National Research
Foundation of Korea, and KOSEF through NRL in Korea.
Motivation I: Assignment of
perturbed spectra
K(4S1/2)+Rb(5PJ)
• Initial state for molecular
beam (MB) spectra is X 1S+,
v=0 and v=1, at low J.
1 1P
15
2 3S+
3
-1
Energy (X10 cm )
• Initial state for ultracold
molecule (UM) spectra is
a 3S+, mainly in v=20 and
v=21, at low J.
b 3P
10
K(4S1/2)+Rb(5S1/2)
5
a 3S+(v, J)
X 1S+(v =0, J )
0
2
4
6
8
10
12
14
16
R (Å)
• Selection rules allow only W=1 for triplet states in the MB spectra,
but W=0,1,2 for UM spectra.
• No rotational resolution due to pulsed laser linewidth, ~ 0.1 cm−1.
18
Motivation II: how to produce
v =0 molecules?
• To date, molecules with T < 1 mK can be produced only by
combining ultracold atoms using photoassociation (PA) or
magnetoassociation (MA).
• Both normally produce levels of very high v.
• Transfer to low v requires either:
1. Unusual PA mechanisms (e.g., FOPA).
2. Resonant coupling of small-R and large R levels due to
electronic perturbations.
3. STIRAP-type Raman transfer. Optimal path often not
obvious. The MB-UM method identifies it automatically.
Experimental scheme for UM (Storrs)
Ionization Continuum
1) PA to form ultracold
KRb*.
REMPI
K(4S1/2)+Rb(5PJ)
e  (v , J )
1 1P
2 3S+
3
-1
Energy (X10 cm )
15
e(v , J )
b 3P
10
Spont. Emission
PA
3) REMPI detection
via intermediate
states e (v, J ) .
K(4S1/2)+Rb(5S1/2)
5
a 3S+(v, J)
X 1S+(v =0, J )
0
2
4
6
8
10
R (Å)
12
14
16
2) Spontaneous
decay into the
triplet ground state,
a 3Σ+.
18
Experimental scheme for MB (Korea)
Ionization Continuum
MB RE2PI
e  (v , J )
1 1P
2 3S+
3
-1
Energy (X10 cm )
15
1) Supersonic beam
forms X 1S+ with
v = 0, 1.
K(4S1/2)+Rb(5PJ)
2) REMPI detection
via intermediate
states e (v, J ).
b 3P
10
K(4S1/2)+Rb(5S1/2)
5
a 3S+(v, J)
X 1S+(v =0, J )
0
2
4
6
8
10
R (Å)
12
14
16
18
Combined UM and MB spectra
Ionization Continuum
UM RE2PI
MB RE2PI
K(4S1/2)+Rb(5PJ)
e  (v , J )
1
1P
e(v , J )
• Comparison
facilitates
assignments.
2 3S+
3
-1
Energy (X10 cm )
15
• Intermediate states
e (v , J ) can
coincide.
b 3P
10
PA
SE
SR1
•
SR2
K(4S1/2)+Rb(5S1/2)
5
a 3S+(v, J)
X 1S+(v =0, J )
0
2
4
6
8
10
R (Å)
12
14
16
18
Multiplicative
spectrum UMMB
identifies Raman
pathway SR1+SR2.
Excitation windows
WMB
WUM
17
1 +
3 S
1
2 P
1
1 P
3
b P
3
-1
Energy (10 cm )
16
Intermediate
level
15
3 +
2 S
1 +
A S
14
13
MB
UM
12
4
6
8
R (Å)
10
12
Complete spectra from the MB and UM
experiments
1.0
Intensity (arb. units)
0.5
UM Spectra
0.0
1
1.0
10
5
v'=0
15
1 P
3
2 S

3
b P
0.5
MB Spectra
0.0
15000
15200
15400
15600
-1
Energy (cm )
15800
16000
• Not shown is b 3P  X 1S+, for
which the FCFs are negligibly
small.
3
3 +
b P (v')  a S (v" = 21)
15500
16000
-1
Energy (cm )
0.3
1
1 +
1 P (v')  X S (v" = 0)
0.2
3 +
1 +
0.1 2 S (v')  X S (v" = 0)
0.0
14000
14500
15000
15500
16000
-1
Energy (cm )
1P
0.015
FCF
• The 1
 X transition has a
larger electronic transition
moment than 2 3S+  X, in
addition to its larger FCFs.
0.008
0.006
0.004
0.002
0.000
15000
FCF
• Calculated from the potential
energy curves of Rousseau,
Allouche, and Aubert-Frécon, J.
Mol. Spectrosc. 203, 235
(2000).
FCF
Franck-Condon factors
0.010
3 +
3 +
2 S (v')  a S (v" = 21)
1
3 +
1 P (v')  a S (v" = 21)
0.005
0.000
15000
15500
16000
-1
Energy (cm )
Central portion, with assignments
Due to singlet-triplet
mixing, the 1 1P1
and 2 3S+1 levels are
evident in both
spectra.
The b 3P1 level is
weak, but
nevertheless visible,
in the MB spectrum.
1
1 P1
3 
2 S 1,0
-
3
b P0,1, 2
UM
1
1 P1
3 
2 S1
3
b P1
MB
15450
15500
15550
-1
Energy(cm )
15600
Avoided crossing near 6.5 Å
16000
1
4(1) 1 P
+
3
b P
1(2)
3(1)
1 +
4(0 ) 3 S
+

3(0 )
3(0 )
-1
Energy(cm )
Avoided crossings
between levels of
equal W cause
anomalous spin-orbit
splittings for large R,
much smaller for the
2 3S+ state than for
b 3P.
15000
3 +
2(1) 2 S

2(0 )
+
1 +
4(0 ) 3 S
14000
1(2)

2(0 )

3(0 ) 3(0+)
3(1)
13000
5.0
5.5
6.0
6.5
R (Å)
7.0
7.5
High-frequency portion, showing reversed
fine structure for the 2 3S+ state
1
1 P1
3 
2 S 0, 1
3
b P0,1, 2
-
UM
1
1 P1
3
+
2 S1
3
b P1
MB
15650
15700
15750
-1
Energy(cm )
15800
15850
Predicted and measured W splitting
-1
Energy Differences (cm )
15
10
Ab initio
5
Experiment
0
-5
13000
14000
15000
16000
-1
Energy (cm )
17000
Vibrational intervals DG from UM spectra
• Agreement of overall trends with
theory shows that the potential energy
curves have the correct shape.
DGv' +1/2 (cm-1)
60
Experiment (This work)
Prior Experiments
Theory (Rousseau et al.)
40
(a)
1 1P
20
0
0
20
40
60
v'
• Agreement with prior experiments for
1 1P is excellent, with just one level in
disagreement.
50
Experiment
Theory (Rousseau et al.)
40
DGv' +1/2 (cm-1)
• Some perturbations and scatter are
evident, due to admixture between
states
(b)
30
2 3 S
20
10
0
0
50
100
150
v'
Prior experiments:
1. N. Okada, S. Kasahara, T. Ebi, M. Baba, and H. Kato,
J. Chem. Phys. 105, 3458 (1996).
2. S. Kasahara, C. Fujiwara, N. Okada, H. Kato, and M.
Baba, J. Chem. Phys. 111, 8857 (1999).
DGv' +1/2 (cm-1)
80
Experiment
Theory (Rousseau et al.)
60
40
(c)
b 3P
20
0
0
50
100
v'
150
200
MBUM product spectra: interpretation
e (v  ,J  )
 
SR2
MBUM
SR1 
a 3S+ (v=21)
X 1S+ (v =0, J =0)
For Raman transfer from a 3S+
(v=21)  X 1S+ (v=0), need an
upper state in common
between both spectra
3 +
2 S1
1
1 P1
3 +
2 S0

3
b P1
3
b P0
3
b P2
UM
Ultracold Molecule intensity:
2
I UM  X , v, J d a e e, v, J  .
Molecular Beam intensity:
2
I MB  X , v  0, J   0 d e X e, v, J  .
1
1 P1
Stimulated Raman rate:
3 +
2 S1
I  a, v, J d a e e, v, J 
3
b P1

e, v, J  d e X X , v  0, J   0
MB
15400
2
15450
15500
-1
Energy (cm )
15550
so I  I MB  I UM .
2
,
MBUM product spectra: results

 
Largest amplitude is via v  =7
of the 1 1P1 state.

MBUM
This level is also noticeably
perturbed on the DG plot
(expanded below.
3 +
2 S1
1
1 P1
3 +
2 S0

3
b P1
3
b P0
3
b P2
UM
60
-1
DGv+1/2 (cm )
v'=0
1
1 P1
3 +
2 S1
3
b P1
5
50
10
40
30
v=7
1
1 P
MB
20
15500
15550
60
-1
Energy (cm )
)
15450
-1
15400
3 +
2 S (W=1)
3
b P(W=1)
15
Summary
• Numerous new assignments to the perturbed 1 1P – 2 3S+ –
b 3P states of 39K85Rb are made by comparing UM and MB
spectra.
• Good agreement with previous experiments (where
available) and with potential curves from Rousseau, et al.
• The MBUM product spectrum automatically selects
optimal pathways for STIRAP transfer of ultracold
molecules to X 1S+, v=0.
• To be published in PCCP special issue (spectra) and JPC
Letters (Raman pathway via MBUM product.)