Interference effect in heavy ion collisions with H2:

By comparing the experimental electron spectrum from atomic H.

L. C. Tribedi.Deepankar Misra , U. Kadhane, Y.P. Singh

Tata Institute of Fundamental Research, Colaba, Mumbai-400 005, India.

Pat Richard, JRM, KSU

P. Fainstein

• Another view

Tata Institute, Mumbai (Bombay)

TIFR On Arabian Sea

Introduction• Detection of low energy electrons emitted in atomic

collisions provide crucial information on the various ionization-mechanisms.

• The e-DDCS spectrum identifies different processes such as soft electrons (SE), electron capture in continuum (ECC) cusp and the binary encounter (BE).

• In addition, the e-spectra from H2, is very rich since it can provide the evidence of the interference effect.

• Since the two H-atoms in molecular hydrogen are indistinguishable, their contributions to the ionization add coherently and an interference effect might be expected.

VOLUME 87, NUMBER 2 PHYS ICAL RE V IEW LETTERS 9 JULY 2001

Evidence for Interference Effects in Electron Emission from H2Colliding with 60 MeVu Kr34+ Ions

N. Stolterfoht et al.

RAPID COMMUNICATIONS

PHYSICAL REVIEW A 67, 030702(R) (2003)

Interference effects in electron emission from H2 by 68-MeV’u Kr33ø impact:Dependence on the emission angle

N. Stolterfoht et al.

Expe

rimen

tal-to

-theo

retic

al ra

tio

Zeff=

1.19

for H

Experimental Details• The electrons emitted from H2 were detected by

an hemispherical electrostatic analyzer between 1 and 1000 eV for 10-12 angles between 150 and 1500.

• We show “fully measured” (Experiment with atomic Hydrogen ) interference oscillation for relatively lower collision energies: 1-2.5 MeV/u C6+ and F9+ on H2/H.

• Also derived the oscillations using Calculated DDCS for H : 6 MeV/u C6+ + H2.

Experimental Setup

F.C.

Slit System

IonizationGauge

Gas InletM.K.S.

HV1 HV2 Vcom

CEM HV& Signal

Turn Table

Shaft

CEMAnalyzer

Turbo

1000 l/Sec

700 l/SecDiff Stack

Block Diagram

CFD TFA BIAS CEM

Computer

F.C.

C.I.

DAC3

DAC1

Scalar

DAC2

DAC4

HV1 HV2Electrostatic

Analyzer

Microcontroller

RS-232

Energy Distribution.

Energy Distribution of secondary

electrons emitted from

H2 by collision with

6MeV/u. bare C ions. 1 10 100 1000

10-6

10-5

10-4

10-3

10-2

10-1

100

101

1 1 0 1 0 0 1 0 0 01 0 -7

1 0 -6

1 x 1 0 -5

1 x 1 0 -4

1 0 -3

1 0 -2

1 0 -1

1 0 0

1 0 1

= 7 5 o

DD

CS

( M

b )

E n e rg y (e V )

E xp t. C D W - E IS

=90o

DD

CS

( M

b )

Energy (eV)

Expt. CDW - EIS

1 10 100 100010-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

1 10 100 100010-5

10-4

10-3

10-2

10-1

100

101

1 10 100 100010-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

1 10 100 100010-6

10-5

10-4

10-3

10-2

10-1

100

101

1 10 100 100010-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

1 10 10010-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

= 45O

CDW - EIS

=60o

=75o

DD

CS

( M

b )

=90o

=110o

Energy (eV)

=135o

Energy Distribution6 MeV/u C6+ + H2

Angular Distribution.

20 40 60 80 100 120 14010-4

10-3

10-2

10-1

100

6 MeV/u C6+ + H2

DD

CS

( M

b )

Angle ()

ev5 ev11 ev31 ev100 CDW-EIS. CDW-EIS. CDW-EIS. CDW-EIS.

Angular Distribution of

secondary electrons

emitted from H2

0 1 2 3 4

1

2

0 1 2 3 40.0

0.5

1.0

1.5

2.0

1 10 100

1x10-5

1x10-4

10-3

10-2

10-1

100

0 1 2 3 4 5 60.20.40.60.81.01.21.4

1 10 100 1000

0 2 4 6 8 10 12 14

0.5

1.0

1.5

2.0 1 10 10010-5

10-4

10-3

10-2

10-1

100

101

(f)

AI peak

1050

D2

D1

(g)

Velocity (a.u.)

1500

(a)

= 450

DD

CS

(Mb)

Energy (eV)

(d)

= 450

DD

CS

Rat

io (R

)

(b)

=75o

Energy (eV)

(e)

=75o

(c)

1050

Energy (eV)

Interference at different angles.

6 MeV/uC6+ + H2

6 MeV/u C6+ + H2.:45o,75o.

0 2 4 6 8 10 12 14

0.4

0.6

0.8

1.0

1.2

1.4

0 1 2 3 4 5 6

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

6MeV/u C6+ + H

2

Expt. CDW-EIS

(b)

ZT=1.19

750

Velocity (a.u.)

6MeV/u C6+ + H2

Expt. CDW-EIS

(a)

ZT=1.19

450

DD

CS

Rat

io (R

)

Dependence of the phase and

amplitude of the oscillation on

different choices of effective target

atomic number (ZT) in the calculation of

DDCS for H.

Interference in backward angles.

0 1 2 3 40.5

1.0

1.5

1 10 10010-5

10-4

10-3

10-2

10-1

100

Expt. CDW-EIS

1500 (b)

RN

Velocity ( a.u. )

6MeV/u C6+ + H

2

Expt. CDW-EIS

(a)1500

DD

CS

(Mb)

Energy (eV)

Frequency of oscillation is higher in backward angles

compared to forward angles, as

predicted by theoretical model.

0 2 4 6 8 10 12 14 16 18

0

200

400

600

800

Dissociation Fractionusing 9 eV proton method1 MeV/u C6++H/H

2

=45o

Df=88%

RF ON RF OFF

Pro

ton

Yie

ld (a

rb. u

nits

)

Proton Energy (eV)

Expt a

t JRML,

KSU

“Fully Measured” interference structure.

0.5

1.0

1.5

2.0

1 10

0.5

1.0

1.5

45o

(a)1MeV/u C6+ + H

2/ H

60o

CDW-EIS

Velocity (a.u.)

(b)

DD

CS

Rat

io (R

)

Fully Measured DDCS Ratio for

H2 & H.

Dependence on projectile atomic

number is investigated.

Accepted in Phys. Rev. Lett. 2004.

Comparison between different methods.

0.5

1.0

1.5

1 100.0

0.5

1.0

1.5

2.0

2.5

1 10 100 100010-6

1x10-51x10-4

10-310-210-1100101

6 8 10 120.5

1.0

1.5

Expt. CDW-EIS

1.5 MeV/uF9+ + H

2 / H

(a)

45o

Expt. CDW-EIS

R

(b)

60o

DD

CS

Rat

io (R

)

Atomic H

BE

Expt. CDW-EISD

DC

S (M

b)

E(eV)

Velocity ( a.u. )

45o

Experimentally measured Cross

section for H was used to derive the interference

oscillations and a comparison was made.

(using theoretical values for atomic H)

Fully Measured DDCS Ratio for H2 &

H.

Absolute DDCS for H and ratio

1 10 100 1000

1

2

310-4

10-3

10-2

10-1

100

1 10 10010-4

10-3

10-2

10-1

100

101

(c)Ratio 60O

DD

CS

( H2 )

/ D

DC

S(H

)

Energy (eV)

B.E.

(b)

DD

CS

(Mb/

eV-s

r)

60O

CDW-EIS FBA

(a)

C6+ + H

30O

Tribedi, R

ichard

et al.

J.Phys.B

(letts.

) 31, L369

1998

The o

scilla

tion i

n the

ratio

was ob

serv

ed b

y us e

ven

earlie

r

Conclusions• Interference effect is not only a phenomena of high energy

collisions. It is important at relatively low collision energies also.

• The dependence of the oscillations on the projectile atomic number is very weak.

• First study of “fully measured” ratios giving a direct evidence of the interference effect.

• Present method is free from:i) the normalization procedure.ii) choice of theoretical parameters like ZT

iii) systematic experimental errors.

[D. M

isra, U

K, YPS, L

CT

Richard, P

F (PRL 2004, in

press)]

References

[1] N. Stolterfoht et al., Phys. Rev. Lett., 87 023201 (2001).

[2] M.E. Gallasi et al., Phys. Rev A 66, 052705 (2002).

[3] L. Nagy et al., J. Phys. B 35, L453 (2002).

[4] Deepankar Misra et al., ( Accepted in Phys. Rev. Lett.,)

6 MeV/u C6+ + H2: 300

0 2 4 6 8 100.0

0.5

1.0

1.5

2.0 Experiment. Model Fitting.

30o

DD

CS

Rat

io

Velocity ( a.u. )

Frequency doubling and Double Scattering.

Single Scattering Double Scattering

1

2

1

2

1

2

(T1+T2)

(T2G0T1) (T1G0T2)

T = (T1+T2) + (T2G0T1 + T1G0T2) + (T2G0T1G0T2 + T1G0T2G0T1) + …T1 = V1 + V1G0V1 +V1G0V1G0V1+…T2 = V2 + V2G0V2 +V2G0V2G0V2+…

k0k0

k0

kk

kk’k’’

k0 = q - k

6 MeV/u C6+ + H2: 600

0 1 2 3 4 5 6 7 8 9

0.50

0.75

1.00

1.25

DD

CS

Rat

io

600

Velocity ( a.u.)

Experiment. Model Fitting.

A double scattering model is

considered. The electrons emitted

from one center get scattered by the

other center, giving rise to a doubling

of the frequency in the interference

oscillations.

Experimental TechniqueElectron spectroscopy:

****C60 vapour source (450-500o C)

*** Hemispherical Electron Analyzer.

*** Preaccleration voltage = +5V

*** metal shielding used to reduce mag. Field (below 5 mG)

*** Gas pressure kept low : 0.1 mTorr

*** electrons between 1 eV to 6 keV

****12 angles between 200 – 1600 degree

Lokesh C Tribedi

Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India

Students: U.Kadhane D. Misra Y.P.Singh, Aditya Kelkar : Post doc: Ajaykumar

Sc. And Tech. Staff : K.V.Thulasiram W. Fernandez And Pelletron Accelerator Staff

X- Ray and electron emission in heavy ion collisions with

fullerenes and solids: The collective response

X-ray set up with Pelletron

14 M

V Pelletr

on Acce

lerator And a LINAC booster coming up

Projectile

Targetn=1

n=2

n=3

Typical Lyman x-ray spectra

1.5 2.0 2.5 3.0 3.5 4.00

100

200

300

400

2.4 2.5 2.6 2.7 2.80

200

400

2.0 2.5 3.0 3.50

100

200

300

110 MeV S16+ on C60(H)

(N)Ly

Ly

Ly

Cou

nts

Energy (keV)Ly

(H)

(N)

C60

N2

C60

Cou

nts

(N)

(H)

(Background)

Energy (keV)

0 5 10 15 20 25 30 35 40

0.15

0.20

0.25

0.3

0.4

0.5

0.6

120 MeV S16+ (b)

I()

/ I()

Target Atomic No.

I(

) / I() Gas targets C

60(a)

Lyman Ratios for gases and C60

The ratio of Ly/ Lyfor solid and gas

GANIL Expt., V=36 a.u.Bare Kr ions on C,Al, Cu and N2 & ArRozet et al.

The Lyman ratio is 20-25%Lower for solids w.r.t gases

Lyintensity for solid and gasEffect of wake field and Stark mixing

Parameters: d, p, s, p

Stark mixing of 2so & 2po in strong wake field (109 V/cm) in a very small time scale 5.10-17sec.

Population changes in 2s and 2p

Metastable 2s

Small 2s-1s M1 transition (3%)Ly enhancement

s 2so, 2po=3.8 eV for S

Wake phenomena and e-density fluctuations: Echenique, Ritchie, Brandt; and Burgdoerfer

Comparison of the ratio i.e. C60 / N2

Difference ~ 15%\i() (for capture)• Model predicts ~ 10%• Other mechanisms: Post

collisional effect!• Effect of Giant dipole polarization

and Stark mixing!

110 120 130 1400.40.50.60.70.80.91.01.11.2

CDW+"Stark-Mixing"

CDW (ion-atom)

16+

13+

Rat

io (R

cg)

Energy (MeV)

Kadhane et al PRL 90

093401 (2

003)

A comparative study

ions Z/ V Quantity Solid st. effect d (s) • Kr36+ 1.0 Ly ratio 20-25% ~ 10-15

• S16+ 1.3 Ly-ratio 15% ~5.10-17

• Cl17+ 1.4 Ly ratio 20 % ~5.10-17

• Si/S/Cl 1.1-1.5 REC 40-50%• C/O/F <0.5-1 REC No measurable effect

Ly ratio in collisions with Cl17+

1 100.2

0.4

0.6

0.8

Dec 2002 run

120 MeV Cl17+

ZT

(Ly

+ L

y )

/ Ly

13 14 15 16 170.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Rat

io(C

60 /

CH

4)

Charge State

D

C60

E-DDCS spectrum of C60

1 10 100 100010-4

10-3

10-2

10-1

100

101

102

103

C60

N2

BE

KLL Auger

45 MeV C6+

= 600 N2

C60

R

el D

DC

S

Energy (eV)

Future?• A new ion source, 14.5 GHz ECR source, (obtained

from Pantechnik, France) will be installed dedicated mainly for atomic collisions in the low energy region.

• It will be coupled with a 300 kV accelerator.• High resolution x-ray, electron spec, ToF• Noble gas cluster/ fullerenes• May be coupled with a laser• ………..• ………..

0 5 10 15 200

100020003000400050006000700080009000

10000

evapnFragmentation

C60

4+

C60

3+Vd = 1800V

Cou

nts

20 30 40 50 60 700

10000

20000

30000

40000

50000

40 50 60

100

1000

10000

100000

C60

2+

C60

1+

Vd = 1800V

Cou

nts

M/q in terms of 12 a.m.u. (No. of C atoms)

36 38 42 44 46 4850 52

54

5856

C60

1+

The Fragmentation Recoil Ion Spectra of C60

Evaporation

Electron density distribution along trajectory in C60

-10 -5 0 5 100

2

4

6

8

10 Impact parameter 9.9 a.u. (<n>=1.366e28 m-3) Impact parameter 9 a.u.(<n>=4.41e28 m-3) Impact parameter 6 a.u.(<n>=3.41e29 m-3) Impact parameter 2 a.u.(<n>=3.086e29 m-3)

Ele

ctro

n D

ensi

ty (i

n a.

u.)

Rparallel

(in a.u.)

Hadjar, Hoekstra, Morgenstern, Schlatholter, PRA 63, 033201 (2001)

1 10

1

10

100

1000

10000

(x 1

0-1

9 c

m2 )

CDW Gas Targets C

60

tot

Target Atomic No. ZT

Total Ly x-ray cross section due to capture

*The CDW over estimates the cross sectionsat v=13

*CDW reproduces the dataat v=36 a.u.

*Higher order terms play a role giving saturation

*The data for C60 falls on “gas-line”

We are at work!! Electron spectroscopy set up

TOFMS

FUTURE PLAN

Electron Spec.

Charge-state

analysis

X-ray

Deepankr

YeshpalUmesh

Umesh