Spectra of dipole bound states and their role in the electron

attachment in interstellar clouds

Felix Güthe1,2

1 Switzerland Ltd., Baden, Switzerland 2 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland

Royal Astronomical Society meeting "Polyatomics and DIBs in Diffuse Interstellar Clouds"

on 8 and 9 Jan at UMIST.

Thanks to :John MaierMarek Tulej

M. V. PachkovThomas Pino

taken from:http://cfa-www.harvard.edu/cfa/mmw/mmwlab/ismmolecules_organic.html

Spectroscopic techniques

Spectral range: UV/visible for DIBs Direct absorption

– I/I0– sensitivity and selectivity– multiple passes and Cavity Ring Down Spectroscopyor

Laser induced Fluorescence • excited state lifetime, fluorescence quantum yield

Mass selective techniques– Resonance Enhanced Multi Photon Ionisation (and related -

R2ColourPhotoDetachment)– change in the m/z ratio (anion neutral ; neutral cation , cation

Fragment)– sensitivity for ion detection is high!– additional molecular information: mass– physics of the ionisation/detachment process is important

C n

C n

C nU ~ 5 0 0 V

t ~ 1 0 s

p ~ 1 0 b a r

1 % C 2H 2 in A r

U

C n

1 2

2 f ix ed

1 sc an n e d

C n

C n

C n + e

Experimental setupresonant two colour photo detachment

R2CPD

10 12 14 16 18 20 22

C10

H-

C13

H-

C7

-

C4-

in

tens

ity

time-of-flight / s

Massspectrum of the ion source

Anion spectroscopy

AA +e-

Photodetachment

threshold

Dipole bound states -DBSs analogous to Rydberg

states for neutrals - large orbital

requires a minimum dipole moment of ~2-2.5 Debye to bind extra electron

ground state or excited state

rovibrationally excited states of the DBS can be unbound

M. Gutowski et al.

PD-Spectra of C2nH- (n=2-4)

1 1+ transitions close to the threshold

(EA). binding energies ~200 -

500 cm-1

for C4H- DBS connected to an excited neutral state

(E(2)> E(2+ )) transitions in the UV (no

DIBs) (<350nm)

28000 28500 29000 29500 30000 30500 cm-1

EA

EA

C4H-

29500 30000 30500 31000 31500 32000

C6H-

30000 30500 31000 31500 32000 32500

EA

C8H-

Origin of C4H- (DBS)

rotational resolution, bent upper state

28630 28640 28650 28660 28670 28680 28690

A = 30.5 cm-1

cm-1

K´=1 K´´=0

K´=0 K´´=0

PD-spectrum of l-C3H2- (DBS)

assigned by:K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996

PD-spectrum with different excitation / detachment lasers

Molecular beam

T= ~50K bound states only visible in upper traces

K-structure of the two strongest vibronic bands

Comparison to DIBs

Comparison to DIBsLaboratory AstronomicalPeak nm DIB (nm) fwhm (nm) EW (mÅ)A1 699.37(7) 699.32(J) 0.096 116

699.318(G)A3 678.81(7) 678.87(J) 0.087 7

678.866(W) 2.3A4 648.97(1) 649.19(J) 0.076 18

648.962(W) 3.6648.929(T) 0.064 6-12

A5 615.21(2) 615,115(T) 0.144 0-15

B12 496.39(30) 496.40(J) 0.063 16

496.389(T) 0.071 31496.390(K)

C1 498.49(15) 498.47(J) 0.065 11

498,478(T) 0.067 19 498.481 (K)

C3 488.74(30) 488,18(J) 0.135 22

488,04(J) 1.97 611488.256(T) 1.49 >466

J=Jenniskens & Desert (1994), G=Galazutdinov et al. http://www.sao.ru/~gala/DIBwavelength.htm, T= Tuairisg et al. (2000), W = Weselak et al. (2000)

All bands in question are narrow only the origin band is considered strong

full PD-Spectrum of l-C3H2-

14000 16000 18000 20000 22000 24000 26000 28000 cm-1

A2A1¬ X2 B

1

B2A"¬ X2 B1

C2A1¬ X2 B

1D2B

1¬ X2 B

1

~~~~

~ ~

~~

H2CCC-

+

recdetcol

-att

-

IkkBkek

=NA

rADDA

rfatt kkk

kkk

Ratio of anions to neutrals

katt= electron attachmentkcol= collisional detachmentkdet= photodetachmentkrec= recombinational detachment

Anion abundance in diffuse interstellar clouds

kf = formation rate temporary negative ion (~r-2)kr= radiative stabilisation (10-1000 s-1 )kDA= dissociative associationkAD= autodetachment

Anion abundance in diffuse interstellar clouds

The capture probablity (kf) of slow electrons by polar neutrals is high

Attachment will be enhanced by rovibrational Feshbach states (“doorway states”)

for fast internal conversion (IC) to the electronic ground state radiative stabilisation (kr) can compete with autodetachment (kAD)

for slow IC the lifetime of the resonance has to be sufficiently long to compete with kAD

Conclusions DIB for l-C3H2

- match not unlikely or disproven. Anion formation is possible for polar molecules

with high EA (as detected by MW spectroscopy)

DBS transitions are strong and in the vis /near UV

Intensity would be only 0.5 % of all DIBs and No. 45 (in intensity) in Jennikens compilation

the most intense DIBs are propably not DBS

Lifetime of rovibrational Feshbach states

400 cm-1 above the binding energy AD could not be observed

at the threshold AD lifetimes must be longer than radiative

stbilisation (kr)

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996

Comparison to Yokohama et al.

R2CPD 50 Kour work

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996

one colour high resolution 500K

15390 15400 15410 15420 15430

1¬0

1¬2

2¬1

3¬2

0¬1

1¬0

1¬2

2¬13¬2

0¬1

0¬0

1¬0

1¬22¬13¬2

0¬01¬0

1¬22¬13¬20¬1

647648649650651

cm-1

Simulation Yokoyama et al.

vibronic shifted by 1117cm-1

5 K 50 K

our spectrum

iodine calibrated 41

0

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996.

H2CCC– :discrepancy between two experiments

let’s compare this: p 10709

overlapping the upper and the lower graph with our data->

15350 15375 15400 15425 15450

1¬0

1¬2

2¬1

3¬2

0¬1

1¬0

1¬2

2¬13¬2

0¬1

0¬0

1¬0

1¬2 2¬1 3¬2

0¬0 1¬0

1¬2 2¬1 3¬20¬1

647648649650651

cm-1

Simulation Yokoyama et al. 5 K 50 K

our spectrum

iodine calibrated 41

0

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996.

H2CCC– : upper graph:ok,but than the frequency and the origin position in Yokoyama et al. disagree

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996.

H2CCC– :discrepancy between two experiments

??lower graph

14280 14290 14300 14310cm-1

Simulation Yokoyama et al. 5 K 50 K

our spectrum no iodine calibration

with scanmate ~1 cm-1

DIB Jenniskens

H2CCC– :origin

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996.

H2CCC– :discrepancy between two experiments

Positions (cm –1) Relative (cm –1)

Label our work Yokoyama et al.our workYokoyama et al.

Assignment

A1 14294.6(1.5*) 14295.68* 0 0 ~A2A1¬

~X2B1:

A2 14498(1.5*) 204 601

A3 14727.6(1.5*) 14735.34* 434 439.66 602

A4 15404.8(0.5) 15412.68* 1111 1117 401

A5 16250.0(0.5) 16260.68* 1956 1965 201

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 1996.

at 14284.42 cm-1

freq. cited

000Iodine calibration

* = estimation

laboratory band DIB (best value) coinc.?699.37(7) 14294.6(1.5) 14295.66 699.32 (J) + (s)678.81 (7) 14727.5(1.5) 14726.29 678.87 (J) ?648.97 (1) 15404.7(0.3) 15404.96 648.962 (W) + (w)615.21 (2) 16250.1 (0.5) 16252.62 615.115 (T) ?

conclusion about coincidence discrepancies:

– our lab -DIB <1cm-1

– our lab -simulation Yokoyama <1cm-1

– precision of our laser (no iodine) ~1cm-1

– our spectrum overlaps with DIB – the position of the DIB has not changed from

Jenniskens to McCall or Galazutdimov the two spectra from p 10709 don’t agree O° is perturbed (p. 10708- paragraph B) O° is not visible in Yokoyama-> How can McCall / Oka rule out the Match ?

PD-spectrum of l-C3H2- and l-C3D2

- (DBS)

14100 14400 14700 15000 15300 15600 15900 16200 cm-1

¯EA

A1

A2

A3

A4

A5

B1

B2 B

3

B4 B

5

B6 B

7

B8

B9 B

10

B11

B12

C1

C3

C4

C5

C6

C7 C

8

A1

A2

A3

A4

A5

610620630640650660670680690700 nm

A2A1¬ X2 B

1 a) H2CCC-

b) D2CCC-

~ ~

Levels of the K-structure

coldest transition belongs to the 0-1 K-stack

B. J. McCall, T. Oka, J. Thorburn, L. M. Hobbs, and D. G. YorkThe Astrophysical Journal, 567:L145–L148, 2002

2002 study on l-C3H2- Bands

B. J. McCall, T. Oka, J. Thorburn, L. M. Hobbs, and D. G. YorkThe Astrophysical Journal, 567:L145–L148, 2002

PD-spectrum of l-C3H2- and l-C3D2

-

(Feshbach states)

18000 19000 20000 21000 22000

B1

B2

B3

B4

B5

B6

B7

B8

B9

B10

B11

B12

C1

C3

C4

C5

C6

C7 C

8

B1

B2B

3

B4

B5

B6

B8

B9

B10

B11

C1

C2C3

C4C

5C

6C

7

b) l-C3D

2

-

a) l-C3H

2

-

wavenumber / cm-1

end C3H2- additional material

Autodetaching states of C3-

410 400 390 380 370 360 350 340 330/nm

Db7Cb6b5b4

b3b2a5b1Ba4a3a2a1 A

neon matrix

gas phase

EA = 1.995eV

Origin bandA2u-X2g

24680 24720 24760 24800

simulation

experiment

wavenumber /cm-1

2591025910 25950 2599025990

=1/2 =3/2

simulation

experiment

15/235/2

oP12

9/2 37/2

sR21

wavenumber /cm-1

Rotational profiles of the band origins

Origin band

B2u--X2g

life time< 5ps

360 350 340 330 320 310 300

E2

E1

D2

D1

C5C

4C3

C2

C1 C2

u

+¬X2g

360 350 340 330 320 310 300

wavelength / nm

C3

-

Autodetaching states of C3-

320 340 360 380 400

000 (c)

000 (a)

C9H

-

wavelength / nm

360 380 400 420 440

000 (c)

00

0 (a)C

11H

-

380 400 420 440 460 480

000 (c)000 (a)C

13H

-420 440 460 480 500 520

000 (c)

00

0 (a)C

15H

-

445 455

R2CPD spectra of the CNH- (odd)

440 420 400 380 360

+(c)

C14

H

/ nm

400 380 360 340 320

(a)0

00

(a)0

00

(c)0

00

C12

H

360 340 320 300 280

(a)0

00

**(c)

00

0

C10

H

590 570 550 530 510 490 470

/ nm

*

(a)0

00

(c)0

00*

C20

H

530 510 490 470 450

(a)0

00

(c)0

00

*C

18H

475 465 455 445 435 425

(a)0

00

C16

H

(c)0

00

R2CPD and Matrix spectra of C2nH-

Two isomers of CNH-

structured band for (c) onlyin gas phase!

intensities can be differed in matrix!

27500 27750 28000 28250

/ cm-1

C10

H26250 26500 26750 27000

C11

H25500 25750 26000 26250

C12

H

Orgins of the CNH- anions

DIB-range

6056524844403632282420 16 12 8 40

5000

10000

15000

20000

25000

30000

35000

HC2n

- (even): 3-

u¬3-

g: ac

E (cm-1)= 4926+259048/N ~2030nm3-

u¬3-

g: cum

E (cm-1)= 10096+182895/N ~990nm

DBS: 1+

u¬1+

g:

E (cm-1)= 34262-22591/N ~292nm~(EA=4.24eV)

HC2n+1

- (odd): 3-

u¬3-

g: ac

E (cm-1)= 8009+178096/N ~1248nm3-

u¬3-

g: cum

E (cm-1)= 14783+129569/N ~676nm

¥

E (c

m-1)

Ncarbon

MH- + e-

MH- +hvis

M- + H

MH*-

(TNI)

(e-), T, (e-)

f, ISRF, EA

k 2,[H,H 2

]

MH-*

MH- +hvis

M- + H

MH + e-

MH- +hIR

k ISC

kAD

kAD,vib

krad,IR

krad,vis

kDA

kDA,RRKM

??

Kinetics of the Anion Chemistry

not included: high energetic radition, shocks, dust grain chemistry

500 510 520 530 540 550 560

560 580 600 620

* *

210

11103

0

110

Wavelength / nm

12103

0

* * *

*

110

130

000

120

Gasphase R2CPD spectrum of C7-

Laboratory

Astronomical

Comparison with astronomical data

1st vibronic band

606.0 606.3 606.6 606.9wavelength / nm

626.8 627.0 627.2 627.4

HD183143 HD50064 CygOB212 HD46711Jenniskens&Desert´94

wavelength / nm

origin band

astronomy

laboratory

560.5 560.9 561.3 561.7wavelength / nm

LAB

wavelength / nm

574.4 574.8 575.2 575.6

end anions additional material