Instrumentation in the Molecular Physics Group

Presented by:

Mats Larsson

Experimental research activities

• Electron-driven molecular processes

• Ultrafast chemical physics

• Spectroscopy of clusters

• (Microwave induced chemistry)

• (Linear ion trap)

• (Biomedical imaging)

Electron-driven molecular processes

• The problem of producing quantum systems (i.e. molecules) in well defined states

• How to produce ionized biological molecules in the gas phase

• How to detect reaction products of electron-driven processes

• How to obtain chemical information

State selected molecular ions• ABC+ (, v, J) • How do we control the internal quantum states?• Excitations can be removed by storage of ABC+

in CRYRING.• This does not always work for J

• This does not work for molecules of type A2+

• This does not work if we want to study ABC+ in a known distribution of excited quantum states

Pinhole discharge source

• Designed and built at UC Berkely

• Characterized at UC Berkeley

• Shipped to Stockholm for experiment at CRYRING

• Shipped back to Berkeley, redesigned, and characterized

• Shipped to Stockholm for new experiment

High pressure

Vacuum

Laser beam for probing

Supersonic expansionincluding ions and neutrals

Discharge

Energy level structure of H3+

Interstellar transitions

2

0

ortho para

Diffuse cloud absorption

Control of vibrational excitation

• Electron-impact source

• Built and characterized at SRI International in Menlo Park, CA

• Shipped AMOLF in Amsterdam and then later to Stockholm

Repeller plates

Extraction Plate

Deflection plates

Hot filament(outside the source)

Electron Trap

Gas Inlet

Ground Plate

• Better control over vibrational populations– Experiments on SEC and DR

– More control over ion source settings

• AMOLF & SRI, Phil Cosby– O2

+() + Cs O2*(Ryd,n=3,’= ) O + O + KER(0-3eV, )

• CRYRING– O2

+ + e- (O2*(Ryd) ) O2** O + O + KER

0 1 2 3 4 5

Kinetic Energy Release--W (eV)

28 mT

7.8 mT

2.3 mT

0.1 mT

0 2 4 6 80 2 4 6 8

1D + 3P3P + 3P3s

g

3d 3p3p

V=0!

V=0,1,2,3!

Ion Source Developments

Biological molecules

In the gas phase

Spray needle :

The needle is inside a nitrogen- gas filled housing for spray stability.

Entrance capillary:

The ion droplets are passing through a heated capillary and evaporate.

Exit:

After the capillary, the ions are stored and

pulsed by a hexapole trap.

experiment

Interaction of biomolecular ions with electrons/photons

Ion trap

Electrospray unit with a pulsed hexapole trap

Quadrople mass filter

MCPs and phosphor screen

HOH

CCD-camera

Beam splitter

Timing(Camac)

Image intensifier

PC

16-segmented PMT

Experimental parameters

• Data taking rate: 600 - 1000 Hz

• Time resolution: 0.6 - 1.0 ns

• Energy resolution: 100 meV

• No chemical information in the standard set-up

Specifications

• Data taking rate > 10 kHz

• Time resolution 1 ns

• Position resolution 0.1 mm

• Dead area 1 cm2

• No chemical information

probe (wlc)sample

flow cell polychromator CCD

pump (shg, thg, topas)

0 1000 2000 3000

0.00

0.02

0.04

550 nm

450 nm

750 nm

tran

sien

t abs

orpt

ion

t (fs)

Example:

I2Br- + h I2- + Br

I2Br-/CH3CN

+

The Cluster Apparatus

The total cluster machine assembly, combining a laser

ablation source with a time-of-flight mass spectrometer

Pressure: 10-4 – 10-7 torr inside the machine

The extracting electric field: static in Stark spectroscopyswitched in lifetime measurements

Cold molecules (Ttrans < Trot < Tvibr < Telectr ) only lowest vibrational and electronic states populated

•Nd:YAG laser (1064 nm) for ablation of the metal clusters

•A tunable ring-dye laser, pumped by an Ar+ laser, for exciting

the molecules.

•The narrow bandwidth cw laser light (FWHM ~ 1 MHz) is

pulsed-amplified in a Bethune cell,

pumped by a XeCl excimer laser (308 nm) pulses 10 ns, ~1 J, FWHM < 150 MHz

•An ArF excimer laser (193 nm) for ionizing the molecules

•Operating frequency: 10 Hz

•Auto-scan system. Iodine calibration spectrum.

Conclusions

• The ion source R&D is probably too specialized to be of interest for an AlbaNova instrumentation project

• The electro-optical part is covered by the KAW application

• From the Molecular Physics point of view, detector development is most suited