Henrik Cederquist, Physics Department, Stockholm University

4th Annual LEIF Meeting Belfast, June 29, 2003

Atomic Physics SU: H. Zettergren, H. T. Schmidt, J. Jensen and H. Cederquist

CEA Ganil: B. Huber, and B. Manil

Aarhus University: S. Tomita, S.B. Nielsen, J. Rangama,

C70 and C60 colliding with slow highly charged ions – a comparison

and P. Hvelplund

C70C60

Part of the team (in Stockholm in December 2002):

P. Hvelplund

J. Jensen

S.B. Nielsen

S. Tomita

J. Rangama

Missing in the picture: H. Zettergren, H.T. Schmidt, and B. Huber

H. Cederquist

C70r+

Important collision features:

Hollow ions and atoms A(q-s)+

E0+E

E0

Aq+

Projectiles:

Xe8+ , Xe16+ , Xe23+ (v= 0.07, 0.10, 0.12 v0)

Targets:

C60, C70 (T=600 °C)

Similarities and differences in ion-induced fragmentation of C60 and C70

C60 C70

Charge stability limits

Kinetic Energy Releases (KER)

Fission barriers

Competition asymmetric fission/evaporation

Fragmentation modes of excited C60 and C70:

Neutral evaporation of small fragments:

Asymmetric fission:

Multifragmentation:

C60 r+ C60-2mr+ + C2m (m=1,2,3,4…)

C60 r+ C60-2m(r-1)+ + C2m

+ (m=1,2,3,4…)

C60 r+ many small fragments in low charge states

C70 r+ C70-2mr+ + C2m (m=1,2,3,4…)

C70 r+ C70-2m(r-1)+ + C2m

+ (m=1,2,3,4…)

C70 r+ many small fragments in low charge states

C60

C70

The experimental technique:

Vex

Multi-hit TDC

START

TRIG

STOP

0 V

-100 V

Collimated C70 Jet

tim

e-of

-fli

ght

Cylindrical analyzer

PSD2

V1

V2

V3

C685+

time-of-flight

Xe23+

21+22+

PSD1

C705+

The C70 powder has high purity (99.4 %)

10 20 30 40

C3+

60

C5+

60

C6+

70

C5+

70

C4+

70

C4+

60

C7+

70

C6+

60

C3+

70

C3+

60

C2+

60

C2+

70

(b)

(a)

m/q (units of C)

Inte

nsi

ty (

arb

. un

its)

Xe8+ - C70 (24 keV)

Xe8+ - C60 (24 keV)

Similarities in the production of intact C60 and C70 ions:

10 20 30 40 70

C7+

70 C5+

70

C8+

70

C5+

70

C7+

70

C6+

70

s=1

s=2

s=3

C8+

70

C7+

70

C6+

70

C5+

70

C4+

70 C3+

70

C4+

70

C3+

70

C2+

70

C4+

70

C+

70

C3+

70

C2+

70

m/q (units of C)

Inte

nsi

ty (

arb

. un

its)

Xe23+ + C70 Xe (23-s)+ + C70r+ +...

10 20 30 60

C8+

60

C7+

60

C8+

60

C6+

60C

5+

60

C7+

60

C5+

60

C6+

60

s=1

s=2

s=3C7+

60

C6+

60

C5+

60

C4+

60

C3+

60

C4+

60

C3+

60

C2+

60

C4+

60

C+

60

C3+

60

C2+

60

Xe23+ + C60 Xe (23-s)+ + C60r+ +...

Relative cross sections for producing intact C70

r+ and C60

r+ ions in Xe23+-C60 and Xe23+- C70 collisions.

0 1 2 3 4 5 6 7 8 9 10

10-3

10-2

10-1

s=1 s=2 s=3

rel

Charge of Cr+

70

0 1 2 3 4 5 6 7 8 9 10

10-3

10-2

10-1

s=1 s=2 s=3

rel

Charge of Cr+

60

C60r+

C70r+

Similarities in the fragmentation of C60 and C70 ions

Maximum fullerene charges

and

4 6 8 10 12

C9+

70

C8+

70

C7+

70 C6+

70

4 6 8 10 12

C7+70C

+5

C2+11

C+11

C+6

C+3

C+4

C2+15 C+

8

C6+70C

9+70

C8+70

C709+

Inte

nsi

ty (

arb

. un

its)

m/q (units of C)

Inte

nsi

ty (

arb

. un

its)

Xe23+ + C70 Xe 20+ + C70r+ +...

GATED!

4 6 8 10 12

C9+

60

C2+

11

C+

6

C+

5C+

3

C+

4

C9+

60C

8+

60

C8+

60

C6+

60 C5+

60

C7+

60C

5+

60

C7+

60

C6+

60

Xe23+ + C60 Xe 20+ + C60r+ +...

GATED!

Light fragments:

C7+

60

C6+

60

C4+

60 C3+

60

C6+

60

C5+

60

C5+

60C

4+

60 C3+

60

10 20

C4+

70

C6+

70

C5+

70

C5+

68

C5+

68

C5+

70C

4+

70

C3+

60

C3+

70

10 20

Xe23+ + C70 Xe 21+ + C70r+ +...

Xe8+ + C70 Xe 6+ + C70r+ +...

Xe23+ + C60 Xe 21+ + C60r+ +...

Xe8+ + C60 Xe 6+ + C60r+ +...

6866

5856

Heavy fragments:

Similarities in kinetic energy releases:

C68(r-1)+

C2+

C58(r-1)+

C2+

Kinetik energy releases – calibration and resolution

Detector

Ion beam

C60+

Collimator

’Cold’ C60-jet (low v(C60))

Xe+

Detector

Ion beam

Warm Xe target (high v(Xe))

~ 3 meV ~ 40 meV

Energy resolution

Energy calibration

Kinetic Energy Releases (KER’s) for C60r+ asymmetric fission –

comparison with other measurements

1 2 3 4 5 6 7 8 90

4

8

12

16

Present expt. data for Xe17+

Scheier et al., MIKE

Senn et al., MIKE

Chen et al., TOF

Tomita et al., TOF

Kin

etic

Ene

rgy

Rel

ease

(eV

)

Charge of final fragment C58

C60r+ C58

(r-1)+ + C2+

KER’s are insensitive to production method!

1 2 3 4 5 6 7 8 90

4

8

12

16 Matt et. al., MIKE Senn et. al., MIKE

Present expt. data for Xe23+

Present expt. data for Xe16+

Kin

etic

Ene

rgy

Rel

ease

(eV

)

Charge of final fragment C68

Kinetic Energy Releases for C70r+ asymmetric fission – comparison with

other measurements (Xe16+ and Xe23+ projectiles)

C70 KER’s are similar for Xe23+ and Xe16+!

2 3 4 5 6 7 8 9 10 11 120

5

10

15

20

25

Xe23+

, C60

Cederquist et al., C60

Present data Xe23+

Present data Xe16+

Kin

etic

En

ergy

Rel

ease

(eV

)

Initial charge of C70/C60, r

C70 data:

C60 data:

Comparisons Kinetic Energy Releases C60/C70 C58(r-1)+

C2+

C68(r-1)+

C2+

U

R

Model:

Differences in fragmentation pathways:

C684+ C68

5+C705+C70

4+

Xe23+ + C70 Xe 21+ + C70r+ +...

C704+ C68

4+ C705+ C68

5+

Xe8+ + C70 Xe 6+ + C70r+ +...

Surprising no such difference for the C60 target!

200 250 300

C5+68

C5+70

200 250 300

C5+68

C5+70

Xe23+ + C70 Xe 21+ +... Xe8+ + C70 Xe 6+ +...

Same comparison - projected distributions:

1 2 3 4 5 6 7 8 90

4

8

12

16

Expt. data for Xe23+

Expt. data for Xe16+

Expt. data for Xe8+

Matt et al., MIKE

Expt. data for Xe23+

Expt. data for Xe16+

Matt et. al., MIKE Senn et. al., MIKE

Kine

tic

Ener

gy R

elea

se

(eV)

Charge of final fragment C68

Note!!

Data for Xe8+ impact!

Conclusions:The relative cross sections for production of intact C60

r+ and C70r+

ions are almost identical as functions of r for a given projectile.

The fragmentation spectra are very similar for C70 and C60 indicating similar roles played by asymmetric fission and evaporation – exception: Enhanced production of C60 from C70

Measured Kinetic Energy Releases (KER) for asymmetric fission C70

r+ C68(r-1)+ + C2

+ are significantly lower than those reported earlier in the literature.

KER’s are close for C60 and C70 ionized by Xe23+ - in agreement with the fission process being controlled by a barrier

4th Annual LEIF Meeting Belfast, June 29, 2003

Fission barriers and stability limits are similar for C60 and C70

C70 in intermediate charge states fission after collisions with Xe16+ or Xe23+ but evaporate after collisions with Xe8+ - new phenomena not observed with C60!

C704+ C68

4+ C705+ C68

5+

Xe8+ + C70 / C60 Xe6+ + C70r+ / C60

r+ +...

C604+ C58

4+ C605+ C58

5+

Note!

Look at the raw data again C60 and C70 really behaves differently with Xe8+ projectiles:

C684+ C68

5+C705+C70

4+

Xe23+ + C70 / C60 Xe21+ + C70r+ / C60

r+ +...

C584+ C58

5+C605+C60

4+

There are some differences even with Xe23+ projectiles:

Fission barriers are lower for C70r+

than for C60r+

C60 C70

Activation energies for neutral C2-emission must be lower for C70

r+ than for C60r+

thus

Ea (C60

r+) = Ea (C60) + (Ik(C58)-Ik(C60) )

k=1

k=r

Ea (C70

r+) = Ea (C70) + (Ik(C68)-Ik(C70) )

k=1

k=r