Gas phase spectroscopy at the CLS

http://www.lightsource.ca

VLS-PGM Beamline

Y Hu et al, Rev. Sci. Instrum. 78 (2007) p083109

VLS-PGM Beamline

VLS-PGM Beamline

Instruments for gas-phase science at the VLS-PGM beamline

Dual toroidal electrostatic analyser

Wiley-McLarentime-of-flightmass spectrometer

Dual toroidal analyser

T J Reddish et al (1997) Rev. Sci. Instrum. 68 2685A E Slattery et al (2000) J. Phys. B. 33 4383

• Toroidal analysers can energy select the charged particles (ions/ electrons) while preserving the initial angle of emission.

• Both analysers are independent and each can be switched to detect electrons or ions.

• Both can operate in threshold (TPES) mode• Detectors can operate in coincidence mode

9 10 11 12 13 14 15 16 170

5000

10000

15000C

ount

s

Binding Energy / eV

Pyridine h = 80eV

Dual toroidal analyser

Dual toroidal analyser

10 12 14 160.0

0.1

0.2

0.3

0.4S

igna

l

Photon Energy / eV

Pyridine TPES

Dual toroidal analyser

12.0 12.2 12.4 12.6 12.8 13.00.0

0.1

0.2

0.3

0.4

Sig

nal

Photon Energy / eV

Pyridine TPES

9.0 9.2 9.4 9.6 9.8 10.00.0

0.1

0.2

0.3

0.4

Sig

nal

Photon Energy / eV

Pyridine TPES

Dual toroidal analyser

1cos3

21

4cos1

42

2

P

dd

Since the toroidal analyser preserves the azimuthal angle of emission of the photoelectron we can find the photoelectron asymmetry parameter across a photoelectron spectrum.

That is we can record “beta paramer” spectra.

The spectra here are beta parameter spectra for H2 and will be the subject of the 2nd half of this talk.

Finally we remember that the detectors can be configured for electrons or ions.

Time of Flight

Electron Start – Ion Stop, with multi-hit electronicsNo energy discrimination on the electron

Allows ToF mass spectra and PePIPICO 2D maps

Time of Flight

0 20 40 60 800

1000

2000

3000

4000

5000C

ount

s

Mass / amu

Pyridazine h=170eV

Parent

“C4”

“C3”

“C2”Water

“C1”

ToF PePIPICO

10000 20000 30000 40000 50000

10000

20000

30000

40000

50000ToF Ion #2

3.621E4

2.559E4

3.935E4

N02 + C3 fragments

C3 + C4 fragments

C + O

(H)CN + NH

(H)CN + C3

(H)CN +C5H5

Mass 29 ?

2 Fragment dissociation = 45

Otherwise could be any angle

0 50100150200250

-NO2

-NO

C5H5

C5H6N

0

50

100

NONO2

ToF

Ion

#1

para-nitroaniline

Time of Flight

http://www.lightsource.ca

If any of this would be of interest to you please talk to me at this symposium.

Michael MacDonaldCanadian Light Source Inc.44 Innovation BoulevardSaskatoon, SK, S7N 2V3306 657 3812

Hydrogen

Hydrogen

HydrogenDirect mechanisms (a) and (b) produce only a limited range of electron energies due to Franck-Condon Factor restrictions

Indirect mechanisms (c) and (d) produce a wide range of electron kinetic energies.

Further mechanism (d) can decay to either the bound σg or dissociative σu state of the ion.

Remember in quantum mechanics indistinguishable paths to the same destination interfere.

Hydrogen

Red – experimental results

Black – full QM closed coupling calculations

Hydrogen

Hydrogen

Results and the simplified model

Summary of H2 results

Unusual properties of observed interference• Interference shows in direction of photoelectrons not

intensity• Direction of photoelectrons are dictated by nuclear

motion (Ultimately it all comes back to symmetry !) • Interference is from different autoionisation paths from a

coherent superposition of electronic states. (Not direct ionisation and autoionisation from a single excited state)

• This is not a coincidence experiment, and, indeed, the oscillations would disappear in a coincidence experiment.

AcknowledgementsDr. Tim ReddishDr. Arathi Padmanabhan

Dr. Smialek-Telega

Prof. Nigel Mason

Dr. Lucia ZuinRu Igarishi

Antonio C.O. Guerra and Cássia C. Turci Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-909, Brazil

Dr. J. FernándezDr. A. Palacios Prof. F. Martín