Transcript colubus2005srsh.ppt

Laser Excitation Spectroscopy
of SrSH and CaSH
By
Michael Dick, P. M. Sheridan, Peter Bernath,
and J.- G. Wang
Motivation – Ca and Sr Polyatomics
 Oxides, halides and hydroxides containing Ca and Sr have been well
studied.
Ca and Sr polyatomics are not as well characterized but are interesting:
Light, few isotopes, main isotopes have no nuclear spin.
Metals ablate easily and form molecules readily.
Follow the progression of electronic states as the symmetry of the ligand
decreases.
SrF
Diatomic
SrCCH
Linear
SrCH3
Symmetric Top
SrNH2, SrSH
Asymmetric Top
While the ground states for many of these polyatomic molecules have been
examined, little or no information exists about the excited states.
~~
CaSH/SrSH A-X
B2 Σ+
~
C 2‘A
A2Π
~
B2‘A
~
A 2‘A
Electronic Transition:
s → pΠ (in plane) promotion on the metal
atom - perpendicular transition
Appearance like a Hund’s case (a) 2 Π Hund’s case (b) 2Σ transition.
Previous Work:
CaSH:
Low resolution by Bernath and coworkers.
High resolution by Bernath and coworkers
SrSH:
Low resolution by Bernath and coworkers.
X 2Σ+
CaF/SrF
Cv
C
v
‘
~2
X
CaSH/SrSH A
Cs
C
s
~~
CaSH/SrSH B-X
B2 Σ+
~
C 2‘A
A2Π
X 2Σ+
~
B2‘A
~
A 2‘A
CaF/SrF
Cv
C
v
‘
~2
X
CaSH/SrSH A
Cs
C
s
Electronic Transition:
s → pΠ (out of plane) promotion on the
metal atom - perpendicular transition
Appearance like a Hund’s case (a) 2Π Hund’s case (b) 2Σ transition.
Previous Work:
CaSH:
Low resolution by Bernath and coworkers.
High resolution by Steimle and coworkers,
including Stark spectroscopy.
SrSH:
Low resolution by Bernath and coworkers.
~~
CaSH/SrSH C-X
B2 Σ+
~
C 2‘A
A2Π
~
B2‘A
~
A 2‘A
Electronic Transition:
s → pσ promotion on the metal atom parallel transition.
Appearance like a Hund’s case (b) 2Σ Hund’s case (b) 2Σ transition.
Previous Work:
CaSH:
Low resolution by Bernath and coworkers.
SrSH:
Low resolution by Bernath and coworkers.
X 2Σ+
CaF/SrF
Cv
C
v
‘
~2
X
CaSH/SrSH A
Cs
C
s
No high resolution work!
The Laser Ablation Source
Preamp
I2 Cell w/ PMT
Single Mode
Ring Dye Laser
Rod Rotator
Scope
Preamp
Boxcar
PMT
Delay Box
Pulsed Valve
Power Supply
Pump
YAG
PC
3rd Harmonic
Trot ~ 4–8 K
Gas mix: 7.5% H2S in argon at a backing pressure of 100 psi.
~ ~
CaSH – C-X
~2
~2
CaSH C A' - X A'
R
P
16072
16074
16076
16078
-1
Wavenumber (cm )
Expected Hund’s case (b) 2Σ - Hund’s case (b) 2Σ structure.
~~
SrSH – C-X
~2
~ 2
SrSH C A' - X A'
R
P
15000
15002
15004
15006
-1
Wavenumber (cm )
Expected Hund’s case (b) 2Σ - Hund’s case (b) 2Σ structure.
~~
C-X Energy Level Diagram
2.5
3.5
2 02
1.5
2.5
1 01
0 00
0.5
1.5
0.5
a
Near Prolate Asymmetric Top:
J
N KK
3 03
c
F2
F1
a – type transitions:
∆Ka=0, ∆Kc=±1
F1
Diagram shows only Ka =0 subband.
Other Ka≠0 subbands possible, but
weaker due to cooling.
R
P
P
Q12
R
R22
R
P22
P
Q21
R11
Ka=0 subband will appear like a
Hund’s case (b) 2Σ - Hund’s case (b)
2Σ transition.
P11
3 03
3.5
2.5
2 02
2.5
1.5
1 01
0 00
1.5
0.5
0.5
a-type transitions
F1
F2
F1
Each rotational level is split into F1 and
F2 components by the spin-rotation
interaction.
CaSH/SrSH – Ka=0 Subband
~2
~2
SrSH C A' - X A'
~2 ~ 2
CaSH C A'-X A'
0.5 P
4.5
Q
12
5.5
1.5
P
1
1.5
P
15002.5
R
R
15003.0
Q
12
0.5
1.5
1
4.5
R 0.5
2
2
0.5 P
4.5
0.5
Q
21
15003.5
-1
Wavenumber (cm )
SrSH
15004.0
P
16074.5
0.5
Q
21
R 0.5
2
2
1.5
16074.0
R
P
1
16075.0
4.5
R 0.5
1
16075.5
16076.0
16076.5
-1
Wavenumber (cm )
CaSH
SrSH - P1/R2 branches smaller spacing, P2/R1 branches larger spacing
CaSH - P1/R2 branches larger spacing, P2/R1 branches smaller spacing
Indicates sign change in spin rotation interaction.
CaSH/SrSH – Ka=1 Subband
~2
~2
SrSH C A' - X A'
~2 ~ 2
CaSH C A'-X A'
0.5 P
4.5
Q
12
5.5
1.5
P
1
1.5
P
15002.5
R
R
15003.0
Q
12
0.5
1.5
1
4.5
R 0.5
2
2
0.5 P
4.5
0.5
Q
21
15003.5
-1
Wavenumber (cm )
SrSH
15004.0
P
16074.5
0.5
Q
21
R 0.5
2
2
1.5
16074.0
R
P
1
16075.0
4.5
R 0.5
1
16075.5
16076.0
16076.5
-1
Wavenumber (cm )
CaSH
Red arrows indicate unassigned lines likely arising from Ka = 1 subband.
Extra lines more apparent in CaSH due to increased signal to noise ratio.
CaSH/SrSH – Molecular Constants
~
C state molecular constants for CaSH and SrSH
~ 2
~ 2
Parameter
(cm-1)
CaSH C A′
SrSH C A′
T
16075.12884(64)
15003.14684(57)
A
(B+C)/2
εaa
(εbb+εcc)/2
Fixed to ground state value
0.144783(15)
0.097114(8)
Fixed to zero
-0.05097(14)
0.06997(10)
Ka=0 subband and pure rotational data fit to Watson’s S-Reduced
asymmetric top Hamiltonian (Pickett’s Program).
The pure precession relationships indicate that (εbb+εcc)/2 should be
negative.
CaSH appears to be following this relationship, while SrSH does not. The
~
C state of SrSH is perturbed.
~~
B-X Energy level diagram
14
c-type transitions
15
13
N J Ka Kc
4 4.5
14
3.5 4
13
12
1 32.5 3
14
3 3.5 1 2
1 11.5 2
12
1 00.5 1
11
13
2 2.5 11 12
1 1.5 11 01
F1
P
P11 QQ11
O
R
P12 PQ12
N
4.5 5
KaKc
R11
Q
R12
P
P22 QQ22
Q
P21
R
R
F2
R22
Q21
S
R21
J
3 03
3.5
2.5
2 02
2.5
1.5
1 01
0 00
1.5
0.5
0.5
F1
F2
F1
c – type transitions:
∆Ka=±1, ∆Kc=0,±2
Diagram shows a Ka(1-0) subband
Ka(1-0) subband will appear like a
Hund’s case (a) 2Π - Hund’s case (b)
2Σ transition.
~
The F1 and F2 components in the B
state will exhibit a large splitting due
to εaa (~ -19.7 cm-1)
Each Ka=1 rotational level is further
split by asymmetry doubling.
~ ~
SrSH – B-X
~2
~ 2A'
SrSH B A" - X
F2
~14825 cm
-1
aa=
~-15 cm
~14810 cm
F1
0
1
2
3
4
-1
5
-1
Relative Wavenumbers (cm )
Each spin component has the expected Hund’s case (a) 2Π - Hund’s
case (b) 2Σ appearance with 1B and 3B spaced branches.
The approximate value of εaa(~ -15 cm-1) is close to that predicted by the
pure precession relation.
-1
SrSH – Assigned Spectrum
~2
~2
SrSH B A" - X A'
F1component
10.5
6.5
5.5
9.5
2.5
2.5
P
1.5
P11
P
Q
Q
Q12
0.5
4.5
1.5
5.5
Q11
R12
R
0.5
R11
O
P12
14811.0
14811.5
14812.0
14812.5
-1
Wavenumber (cm )
Lower state combination differences confirm the above assignments.
The F2 component has not yet been assigned.
~~
A-X Energy level diagram
14
15
4 4.5
13
13
14
14
3 3.5 1 2
13
1 11.5 2
12
F2
F1
P
3.5 4
12
1 32.5 3
2 2.5 11 12
1 1.5 11 01
1 0.5 11 01
N J KaKc
P11 QQ11
O
R
P12 PQ12
N
4.5 5
R11
Q
R12
P
Q
P22 Q22
Q
P21
R
R
R22
Q21
R21
3 03
3.5
2.5
2 02
2.5
1.5
1 01
0 00
1.5
0.5
0.5
b-type transitions
Diagram shows a Ka(1-0) subband
Ka(1-0) sub band will appear like a
Hund’s case (a) 2Π - Hund’s case (b)
2Σ transition.
~
The F1 and F2 components in the A
state will exhibit a large splitting due
to εaa (~ 19.7 cm-1)
S
J
KaKc
b – type transitions:
∆Ka=±1, ∆Kc=±1
F1
F2
F1
Each Ka=1 rotational level is further
split by asymmetry doubling.
~~
SrSH – A-X
~ 2A' - X
~ 2A'
SrSH A
F1
F2
aa = ~5 cm
14274
14276
14278
-1
14280
14282
14284
-1
Wavenumber (cm )
The approximate value of εaa(~5 cm-1) is not close to that predicted by the
pure precession relation(~19.7 cm-1).
Perturbation Summary
~
The εaa value of the A state of SrSH is reduced from ~19.7 cm-1 (pure
~
precession) to ~5cm-1. A similar reduction was also observed in the A state of
CaSH.
~
~
Reduction in CaSH attributed to orbital mixing of the A and C states.
~
This may contribute to the change in sign of (εbb+εcc)/2 in the C state of
SrSH.
~
The B state of SrSH appears to be less perturbed as the calculated
εaa(-19.7 cm-1) is close to the observed value (-15 cm-1)
More work is needed to fully understand these various perturbations.