1 Zeeman patterns in FT resolved fluorescence spectra of NiH Amanda Ross, Patrick Crozet, Heather...
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Transcript of 1 Zeeman patterns in FT resolved fluorescence spectra of NiH Amanda Ross, Patrick Crozet, Heather...
Zeeman patterns in FT resolved fluorescence spectra of NiH
Amanda Ross, Patrick Crozet, Heather Harker and Cyril Richard
Laboratoire de Spectrométrie Ionique et Moléculaire (LASIM),Université Lyon 1 & CNRS, 69622 Villeurbanne, France.
and
Stephen Ashworth
School of Chemistry, University of East Anglia, Norwich NR4~7TJ,UK
Illustrating electronic structure variations in Doppler-limited spectra.
0,72 T
0.13 T
0 T
17408.5 17409.5 cm-1
2
FT Zeeman experiment. LIF + Nd-Fe-B magnets
External magnetic field
fluorescence
Linearly polarisedlaser beam
FTS
Polariser (optional)
Cu anode
Ni cathode
Adjustable gap
3
Zero-field NiH fluorescence spectrum (FT)
Isotopic selection is possible.
Res. 0.05 cm-1, Rec. time 2 hrs.
Abundant rotational relaxation in B state.Strong, collisionally induced fluorescence
4
Emission from excited states E ~17400 cm-1 in NiH
Observe fluorescence from to spin-orbit mixed, and states.
Laser pumps a chosen J
and parity (sometimes)
level of v=1, B 25/2 58NiH
Collisional energy transfer
populates many more!
Q1: Are the Zeeman
patterns useful?
Q2 : Can we model them?
Q3: Is this process MJ
selective?
Emission to X 25/2, v=0-3
E cm-1
5
Some lines show more ‘potential’ than others
R branch, B-X1 58NiH, observed as rotational relaxation
when laser pumped Q(2½) B-X1. Resolution = 0.025 cm-1 , field = 0,72 T
6
The strongest line in the spectrum Q(2½) B 25/2-X1 25/2
happens to have unresolved MJ structure (and doubling)
MJ = 0, ±1
MJ = 0 MJ = +1
Dispersed fluorescence shows all allowed transitions
MJ = -1
Convenient for magnetic field calibration!
LASER
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Pumped Q(2 ½) MJ=0 B= 7200 Gauss
17408.5 17409.0 17409.5 cm -1
Calc. MJ=±1
P(3½) [1-0] line, B 25/2–X 25/2 58NiH
Calc MJ=0
FTS, ~ Doppler limited spectrum
Landé factors are known : McCarthy et al JCP 107 4179 (1997)
+1/2
-3/2
+3/2
+5/2
+7/2
-1/2
-7/2
-5/2
-3/2
-1/2
+1/2 +3/2
MJ" -1/2 +1/2
-5/2 +5/2
+3/2-3/2
17408.6 17409.0 17409.4 cm -1
17408.6 17409.0 17409.4 cm -1
MJ"
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Can we select MJ components ? P(3½) B-X1 again
Near laser, to v"=0Transition to X1 v"=2
Populate all MJ’
- 2½ ≤ M J' ≤ 2½
Popu1ate all MJ’ except MJ2½
Laser(scatter)
Populate only MJ' = 2½
MJ" = 3½
1½
2½
0.72 T
0.73 T
Caveat :even uglier because of the onset of doubling
9
MJ is enhanced even after collisions (J+1) within a given state
0.7 T
10
Simplify by recording fluorescence through a polarizer. Example : collisionally induced fluorescence, R head, F 27/2 -X1 25/2
R(J") 2.5 3.5
6.5 5.5 4.5
MJ = 0
MJ = ± 1
MJ = 0, ± 1
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Another example where the polariser really helps
P(3½) B 25/2 – X1 25/2 P(3½) I – X2
23/2
all
MJ 0, ± 1 can be distinguished for some ‘new’ transitions
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Zeeman structure does not always collapse at high J
Example : P branch, I – W 23/2
Pf (6½) Pe (6½)
0.72 Tesla
13
Any new results ?
58NiH : extension to v" =1, 2 in X125/2 , X2
23/2 and to v=1 in
the W1 23/2 state.
60NiH : a lot of measurements …
Fit ~ 1100 transitions (from 2 spectra) to simple expression
to find T, geff(J, parity)
Effective Landé factors geff can be predicted from the Field group
Supermultiplet model (zero field fit) & Zeeman Matrix.
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Spin-Orbit Coupling + L and S uncoupling off diagonal matrix elements
v 0 Idem x FC factors
Current fit status : unstable !
2+ 21/2 23/2
23/2 25/2
2+ Spin-Orbit A.L.S
Rotation 2.L.S -2.J.S - 2 J.L
Rotation - 2 J.L
21/2 Rotation -2.J.S Rotation - 2 J.L
23/2 Rotation 2.L.S
Rotation - 2 J.L
23/2 Spin-Orbit A L.S
Rotation -2.J.S
25/2
Supermultiplet model given by Gray et al, J. Chem. Phys 95 7164 (1991)
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Zeeman matrix, at given J.
1/2 3/23/2 5/2
gs
(6/2) . J(J+1)-3/4
1/2 gs
gs J(J+1)-3/4
2 J(J+1)-15/4
J(J+1)-15/4
3/2 gs
gs J(J+1)-15/4
2
3/2 gs
5/2 gs
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Satisfactory outcome … Example, W1, 23/2
v=0 2
v=0 69 67
v=0 6 6
v=1 1
v=1 0 2 79
v=1 20 20 8
v=2 2
v=2 8
% Composition Parity e f e
f
Pe( 5½)
I – W1 (0-0)
Pf (5½)
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Comments, Conclusions and Acknowledgements
Isotopic selectivity is a real advantage.
Collecting all data in identical conditions is great!
S/N ratio is a problem, particularly with single MJ selection
Polariser alignment is critical.
Analysis is the rate determining step.
We are grateful to the CNRS and to ANR for the financial support received for this project.
Many thanks for comments, encouragement and suggestions from R. Field, D. Tokaryk, C. Linton, T. Steimle, A. Ariste-Lopez …
18
More examples in collisionally induced systems Q branch of F 27/2 -X1 25/2 and R branch of A 25/2 -X1 25/2
Analysis of Zeeman structure gives g ~ 3 for F 27/2 , as expected; but g ~ 2 for A 25/2 . Already established by RWF and coworkers …
0.71 Tesla
Zero field
Resolution 0.02 cm-1.330 scans
12000 – 17500 cm-1