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

7

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"

8

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

11

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

12

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.

14

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)

15

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

16

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)

17

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