Current Research and Future Plans - IISER Punebhasbapat/bapat_files/140127_iiserp.pdf · Current Research and Future Plans Bhas Bapat PRL, Ahmedbad At IISER Pune, Jan 2014 Bhas Bapat

Current Research and Future Plans

Bhas Bapat

PRL, Ahmedbad

At IISER Pune, Jan 2014

Bhas Bapat (PRL, Ahmedbad) Current Research and Future Plans At IISER Pune, Jan 2014 1 / 21

Contents

Broad Areas

Dissociative Ionisation

Photoionisation of CS2

Summary

What Next?

Plans for IISER-Pune


Broad Areas

I Kinematically complete dissociative ionisationI Major part: high energy electron-impact on moleculesI Technique: ion-momentum spectrometry/coincidence momentum imagingI Successes: identification of bent states of CO2+

2 and determining thelifetimes of metastable states

I Similar experiments using photons (Indus-1) and fast high charge ions(IUAC)

I Inverse kinematics is probably the only way to access the dynamics oftransient molecular ions in conjunction with the computation of PE surfaces

I Production of clusters (single/mixed species) with a goal to studyheterophase photochemical reactions

I cluster production by sputtering and laser ablation, mass spectrometricdetection

I only minor success overallI State selective dissociative ionization

I electron–ion multi-fold differential cross-sections[correlated momentum maps]

I under photo-absorption (as well as ion impact)


Broad Areas Instrumentation

Instruments built over the last few yearsI Ion momentum spectrometers with coincidence momentum imagingI Time-of-flight mass spectrometerI Ion sputtering cluster source, laser ablation cluster source, supersonic

nozzle beam cluster sourceI Cylindrical Retarding Potential analyser (space instrumentation)I A combined Cylindrical Mirror Analyser for electrons and Ion Momentum

Spectrometer


Dissociative Ionisation Complete Kinematics

B+

A+

(A+B)2+

I No exact solutions to the multi-electron Hamiltonian; only approximatecalculation of the transition matrix

I Measurement of DCS enhances our understanding of the dynamicsI Fragment kinematics are leads to properties of the transient stateI Experimental Challenge: detect all fragments and determine the

correlated kinematics of all fragments – ions, atoms and electronsI Additional consideration: the transient state is not unique


Dissociative Ionisation Complete Kinematics

B+

A+

(A+B)2+

I No exact solutions to the multi-electron Hamiltonian; only approximatecalculation of the transition matrix

I Measurement of DCS enhances our understanding of the dynamicsI Fragment kinematics are leads to properties of the transient stateI Experimental Challenge: detect all fragments and determine the

correlated kinematics of all fragments – ions, atoms and electronsI Additional consideration: the transient state is not unique


Dissociative Ionisation Selectivity in excitation

internuclear coordinate

ener

gy

excitation

ionisation

dissociativeionisation

ground state

+

++ + +

dissociation

I Dissociation patterns expected todepend on which molecular stateis accessed by the excitation

I Can we control or select theexcited state that participates inthe DI process?

I Such selectivity will bring uscloser to measuring the fullydifferential cross-section to enablea direct comparison with theory

I Selectivity can be brought in byobtaining correlated ionmomentum distributions inconjunction with ejected electronenergies




ener

gy

excitation

ionisation


ground state

+

++ + +

dissociation








ener

gy

excitation

ionisation


ground state

+

++ + +

dissociation






Dissociative Ionisation Strategy

AB −→ ABn+ + 2e− −→ fragments + 2e−,n ≥ 2











Dissociative Ionisation Apparatus

Gas

Jet

Ion Drift Tube(TOF)

CMA

Interaction Region

e- - ion coincidence

Position Sensitive Detector

I Crossed photon and molecular beams, single collision conditionsI Ion momentum spectrometer augmented with the CMAI Electrons of specific energy, selected by the CMA, start the ion TOF clock


Photoionisation of CS2 S-L2,3 resonant absorption

05 0 0

1 0 0 01 5 0 02 0 0 0

05 0 0

1 0 0 01 5 0 02 0 0 0

02 0 04 0 06 0 0

2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 00

5 0 0

1 0 0 0

O 2+

N 2+

C S 23 +

C S 22 +

C S +O + / S 2 +

C +S +( 3 h - 1 p )

6 σg−2 / 5 σu

−2 / 6 σg−1 5 σu

−1

6 σg−1 2 πg

−1 / 5 σu−1 2 πg

−1 / 2 πg−1 2 π u

−1

2 πg−2

Coun

ts (ar

bitrar

y unit

s)

T i m e o f f l i g h t ( n s )



05 0 0

1 0 0 01 5 0 02 0 0 0

05 0 0

1 0 0 01 5 0 02 0 0 0

02 0 04 0 06 0 0

2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 00

5 0 0

1 0 0 0

O 2+

N 2+

C S 23 +

C S 22 +

C S +O + / S 2 +

C +S +( 3 h - 1 p )

6 σg−2 / 5 σu

−2 / 6 σg−1 5 σu

−1

6 σg−1 2 πg

−1 / 5 σu−1 2 πg

−1 / 2 πg−1 2 π u

−1

2 πg−2

Coun

ts (ar

bitrar

y unit

s)

T i m e o f f l i g h t ( n s )



05 0 0

1 0 0 01 5 0 02 0 0 0

05 0 0

1 0 0 01 5 0 02 0 0 0

02 0 04 0 06 0 0

2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 00

5 0 0

1 0 0 0

O 2+

N 2+

C S 23 +

C S 22 +

C S +O + / S 2 +

C +S +( 3 h - 1 p )

6 σg−2 / 5 σu

−2 / 6 σg−1 5 σu

−1

6 σg−1 2 π g

−1 / 5 σu−1 2 π g

−1 / 2 π g−1 2 π u

−1

2 π g−2

Coun

ts (ar

bitrar

y unit

s)

T i m e o f f l i g h t ( n s )Bhas Bapat (PRL, Ahmedbad) Current Research and Future Plans At IISER Pune, Jan 2014 11 / 21


3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0

0 . 0 0 0 0 . 1 0 0 0 0 . 2 0 0 0 0 . 3 0 0 0 0 . 4 0 0 0 0 . 5 0 0 0 0 . 6 0 0 0 0 . 7 0 0 0 0 . 8 0 0 0 0 . 9 0 0 0 1 . 0 0 0

3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0

Time o

f fligh

t Hit2

(ns)

3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0

2 0 0 0 2 5 0 0 3 0 0 0

3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0 ( 3 h - 1 p )

T i m e o f f l i g h t H i t 1 ( n s )

2 πg−2

6 σg−2/ 5 σu

−2/ 6 σg−15 σu

−1

6 σg−12 πg

−1/ 5 σu−12 πg

−1/ 2 πg−12 πu

−1

C +

S +

S +

C S +



3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0

0 . 0 0 0 0 . 1 0 0 0 0 . 2 0 0 0 0 . 3 0 0 0 0 . 4 0 0 0 0 . 5 0 0 0 0 . 6 0 0 0 0 . 7 0 0 0 0 . 8 0 0 0 0 . 9 0 0 0 1 . 0 0 0

3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0

Time o

f fligh

t Hit2

(ns)

3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0

2 0 0 0 2 5 0 0 3 0 0 0

3 2 5 03 5 0 03 7 5 04 0 0 04 2 5 0 ( 3 h - 1 p )

T i m e o f f l i g h t H i t 1 ( n s )

2 πg−2

6 σg−2/ 5 σu

−2/ 6 σg−15 σu

−1

6 σg−12 πg

−1/ 5 σu−12 πg

−1/ 2 πg−12 πu

−1

C +

S +

S +

C S +



I A three-body break-up is coplanarI Dalitz Plot : correlated momentum

of the three fragments in terms ofreduced energy

I Visualize precursor ion geometryat the time of break-up



I A three-body break-up is coplanarI Dalitz Plot : correlated momentum

of the three fragments in terms ofreduced energy

I Visualize precursor ion geometryat the time of break-up


Photoionisation of CS2 Conformation Changes

CS2+2 (3h − 1p) −→ C+ + S+ + S

CS2+2 (3h − 1p) −→ C + S+ + S+

0.0

0.0

0.10000.25170.40330.55500.70670.85831.010

0.0

0.0

-0.4

-0.2

0.0

0.2

0.4

C : S+: S+C+: S+: S

DalitzX (arbitrary units)DalitzX (arbitrary units)

DalitzX (arbitrary units)0.0

-0.4

-0.2

0.0

0.2

0.40.0

(b)(a)

Dal

itzY

(arb

itrar

y un

its)


Summary

I Branching ratios of dissociation channels are highly dependent on thetransient molecular ion state

I Fragment ion kinematics clearly show effects of shell selective excitation,interpreted in terms of the energy sharing between the ejected electronsand molecular ion, and the subsequent conformal changes in themolecular ion

I These results bring us closer to being able to make a comparisonbetween measured and computes differential cross-sections

Review of Scientific Instruments, 84 073101 (2013)

Journal of Chemical Physics, 139 164309 (2013)


Summary

I Branching ratios of dissociation channels are highly dependent on thetransient molecular ion state

I Fragment ion kinematics clearly show effects of shell selective excitation,interpreted in terms of the energy sharing between the ejected electronsand molecular ion, and the subsequent conformal changes in themolecular ion

I These results bring us closer to being able to make a comparisonbetween measured and computes differential cross-sections

Review of Scientific Instruments, 84 073101 (2013)

Journal of Chemical Physics, 139 164309 (2013)


What Next? This Field

I Improve on the shell-selectivity – by better electron analysis and asmarter correlation strategy, higher photon energies, better energyresolution

I Orientation effects and angular distributions with shell selectivity to beexplored

I Other perturbation regimesI Ion impact studies of similar type (MeV class ion accelerator: IUAC)I These effects in intense laser fields

I Look into applications of ion–ion correlation mappingI Inspiration: stopping power studies from the 1960s has benefited isotope

geochronology via accelerator mass spectrometryI Inspiration: atmospheric aerosol analysis has benefited from high resolution

ToF-MS


What Next? This Field

I Improve on the shell-selectivity – by better electron analysis and asmarter correlation strategy, higher photon energies, better energyresolution

I Orientation effects and angular distributions with shell selectivity to beexplored

I Other perturbation regimesI Ion impact studies of similar type (MeV class ion accelerator: IUAC)I These effects in intense laser fields

I Look into applications of ion–ion correlation mappingI Inspiration: stopping power studies from the 1960s has benefited isotope

geochronology via accelerator mass spectrometryI Inspiration: atmospheric aerosol analysis has benefited from high resolution

ToF-MS


What Next? Plans for IISER-Pune

I Teaching Plans : (re-)building classic experiments that form the bedrockof modern science, for interpretation by undergraduate students

I Positron and Positronium collisions with moleculesI Cross-disciplinary studies




I Positron and Positronium collisions with molecules

I Cross-disciplinary studies




I Positron and Positronium collisions with moleculesI Cross-disciplinary studies


Plans for IISER-Pune Teaching-related plans

I Development of laboratories for undergraduate teaching that foreseeI interesting and challenging experiments in normal coursesI Re-building classic experiments that form the bedrock of modern science, for

interpretation by undergraduate studentsI lead time of about two years

I In the long run:I public outreach, attracting college teachers etcI become a nodal centre supporting experimental activities for undergraduate

Physics courses throughout the country, and bring a unique distinction toIISER Pune


Plans for IISER-Pune Positronium–molecule scattering

I Electrons and positrons scatter differently from atoms molecules –theoretically well understood with fair experimental evidence in support

I Intriguingly, the positronium – a positron-electron bound state – has beenfound to scatter from molecules in a manner similar to electrons

I Positron and positronium sources are scarce – validation of experimentaldata is a hurdle; experiments continue to show interesting features

I Experimental facility is complex and lead time likely to be longI Diagnostics used for electron collisions are readily applicable to positron

collisions, and to a lesser extent to positronium collisionsI Only two or three facilities world-wide for such studies, none of them in

India.


Plans for IISER-Pune Cross-disciplinary studies

I Experimental research at IISER Pune having a common knowledge baseand technology

I plasmonics, nanophotonics, nanotechnology, magnetic systems, surfacescience, precision spectroscopy, quantum optics,

I gas phase laser spectroscopy and photoionization dynamics of biologicallyrelevant molecules

I Common thread: ever deeper understanding of the interaction of lightwith matter in a wide gamut of characteristics of the light

I Develop a long term programme initially focusing on laser–matterinteractions in the strong field, short pulse regime

I A femto-second high power laserI A pulsed noble gas cluster source for HHGI A monochromator for the resulting VUV and XUV radiation pulses



















I Opens up the possibility of time-resolved or ultrafast probing of moleculesand condensed matter

I The monochromatic, short pulse length XUV radiation source would beuseful for condensed matter studies, mainly for investigating electroncorrelations and and magnetisation dynamics in real-time

I Can also be a source of pulsed high energy electrons with unusualproperties – could be suitable for electron microscopy of surfaces andnanoparticles


Documents

Current Research and Future Plans - IISER Punebhasbapat/bapat_files/140127_iiserp.pdf · Current Research and Future Plans Bhas Bapat PRL, Ahmedbad At IISER Pune, Jan 2014 Bhas Bapat