Laboratory and Astronomical Detection of

CCCN¯

P. Thaddeus, C. A. Gottlieb, H. Gupta, S. Bruenken, M. C. McCarthy, M. Agundez, M. Guelin, and J.Cernicharo, Astrophysical Journal 677, 1132 (2008)

Background

CCCN radical (X2Σ)

Isoelectronic with CCCCH

First observed in space (Guelin and Thaddeus1977)

Glow discharge (Gottlieb et al. 1983)

Supersonic beam (McCarthy et al. 1995)

LIF spectrum (358 nm; Hoshina and Endo, JCP 2007)

CCCN¯ in space

Herbst (Nature 1981)

Petrie and Herbst (ApJ 1997)

• Anions in the laboratory6 anions now detected

• Anions in space4 anions detected with surprisingly high abundances

• Conclusions

Spectroscopic Properties of CCCN¯ CCCN¯

Binding energy one of highest (4.58 eV)

Closed shell 1Σ

No high-resolution spectroscopy

Dipole moment (3.1 D)

Spectroscopic enhancement ~2.4

High-level quantum calculations Gupta and Stanton (2007) Kolos, Gronowski, and Botschwina (JCP 2008)

Spectral Compression

Laboratory Measurements

Experiment: Results:

Glow discharge (~20 mA) 12 transitions observed HCCCN (Ar or N2) 97 - 378 GHz

Concentration: 2 constants: B and D CCCN-/CCCN ~1%

Mole fraction: rms = 19 kHz

~5 x 10-8

(3 - 10) x 10-6 HCCCN

Other sources:

HCCH/N2

Evidence for CCCN¯ CCCN¯

A. Experiment

Closed shell ground state B within 2% of CCCN Ion drift

B. Spectroscopic

Measured vs theoretical: B and D

eQq (McCarthy and Thaddeus FC04; JCP 2008)

Ruled out:

isotopic CCCN

vibrationally excited CCCN

CCCN+

radiation

Ion Drift Measurements

--

----HV

--

---+HV

Single pass absorption with alternating polarity

Spectroscopic Constants

_______________________________________________________ Theoretical ______________________Constant Measured This work KGB

_______________________________________________________B 4851.62183(20) 4848 4850106xD 685.92(10) 627 628eQq -3.248(5) -3.3 …_______________________________________________________

Evidence for CCCN¯ CCCN¯

A. Experiment

Closed shell ground state B within 2% of CCCN Ion drift

B. Spectroscopic

Measured vs theoretical: B and D

eQq (McCarthy and Thaddeus FC04; JCP 2008)

Ruled out:

isotopic CCCN

vibrationally excited CCCN

CCCN+

Formation in Glow Discharge

I. Dissociative electron attachment:

A. CN¯ e¯ + NCCN CN¯ + CN

(Tronc and Azria, CPL, 1982)

(Kuhn, Fenzlaff, and Illenberger, CPL, 1987)

B. C2nH¯ e¯ + HC2nH C2nH¯ + H

[May et al., Phys. Rev. A 77, 040701 (2008)]

C. CCCN¯ e¯ + HCCCN CCCN¯ + H

(Graupner et al., New J. Phys., 2006)

II. Other mechanisms?

CCCN¯ in Space

IRC+10216

4 lines observed: 97, 106, 135, and 145 GHz rms = 0.4 MHz

Intensities No missing lines Spectroscopic constants

Constant (MHz) Laboratory Astronomical

B 4851.62183(20) 4851.61(3)

106 x D 685.92(10) 700(100)

Abundances in Space

TMC-1 IRC+10216

Anion/Radical# obs. calc. obs. calc.

CCCN¯ <0.8a 1b 0.52a

C4H¯ <0.014c 0.2d 0.024e 0.8d

C6H¯ 1.6c 8.9d 8.6f 30d

C8H¯ 5c 5.4d 28/37g 28d

#All ratios in %

a This work; b Petrie and Herbst, ApJ 1997; c Bruenken et al. 2007; d Millar et al. ApJL 2007; e Cernicharo et al. ApJL 2007; f Kasai et al. ApJL 2007; g Remijan et al., ApJL 2007; Kawaguchi et al., PASJ 2007.

Properties of anions

• closed-shell 1S ground states and large dipole moments

(m)

• large electron affinities (EA)

• radicals are observed in astronomical sources

• anions do not react with H2 Barckholtz et al., ApJL 2001EA (eV) m (D) m (D) B (MHz)

CCH 2S 2.97 0.8 CCH¯ 1S 3.1 41,639

C4H 2S 3.56 0.9 C4H¯ 1S 6.1 4,656

C6H 2P 3.81 5.6 C6H¯ 1S 8.2 1,377

C8H 2P 3.97 6.3 C8H¯ 1S 11.9 583

CN 2S 3.8 1.5 CN¯ 1S 0.7 56,133

C3N 2S 4.59 2.9 C3N¯ 1S 3.1 4,852

mm-wave absorption spectrometer

InSb detector

LN2 LN2

solenoid

2 m

power supply

Gunn × n

• low current dc glow discharge [C2H2 (85 %) + Ar (15 %)]

• frequency coverage: 70 – 900 GHz

• frequency accuracy: 10 – 50 kHz

• cell walls cooled: 100-300 K