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CHARACTERIZATION AND FORMATION PROCESSES OF C 4 -, C 4 H and C 4 H - M. L. SENENT Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura.

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Presentation on theme: "CHARACTERIZATION AND FORMATION PROCESSES OF C 4 -, C 4 H and C 4 H - M. L. SENENT Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura."— Presentation transcript:

1 CHARACTERIZATION AND FORMATION PROCESSES OF C 4 -, C 4 H and C 4 H - M. L. SENENT Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, C.S.I.C., Serrano 121, Madrid 28006, SPAIN V. BRITES, M. HOCHLAF Universitè Paris-Est, Laboratoire de Modèlisation et Simulation Multi Echèlle, MSME FRE 3160 CNRS, 5 boulevard Descartes, Marne-la-Vallèe, FRANCE

2 Motivation: astrophysical observations (Scientific preparation of Herschel and ALMA) The starting point of our carbon chains study was the tentative detection of C 4 with the ISO observatory. 1) Recent interest for anions: the detection of C 6 H - (McCarthy et al. 2006) provoques the search of anions in ISM and CSM (C 4 H -, C 8 H -, C 3 N -,C 5 N - ) 2) Recent detection of C 4 H - (Cernicharo et at. A&A 2007)

3 OUTLINE 1)C4 -, C 4 H and C 4 H - structures: isomers 2)Spectrocopic properties 3)Formation processes

4 References M.L. Senent and M.Hochlaf, Astrophys. J., (2010)Astrophys. J., (2010) M. Hochlaf et al. (in preparation) Previous papers: H.Masso et al. J.Chem.Phys (2006)J.Chem.Phys (2006) N.Inostroza et al. A&A (2008)A&A (2008) Theory : Main part: RCCSD(T)/aug-cc-pVQZ Dipole moments with CASSCF/aug-cc-pVQZ Excited electronic states MRCI/aug-cc-pVQZ MOLPRO 2006

5 C4C4C4C4 C4+C4+C4+C4+ C4-C4-C4-C4- C4HC4HC4HC4H C4H-C4H-C4H-C4H- C 3 Si isomers

6 C4C4C4C4 C4+C4+C4+C4+ C4-C4-C4-C4- C4HC4HC4HC4H C4H-C4H-C4H-C4H- C 3 Si Relative energies (eV)

7 C4C4C4C4 C4+C4+C4+C4+ C4-C4-C4-C4- C4HC4HC4HC4H C4H-C4H-C4H-C4H- C 3 Si Ground electronic state: S (singlet); T (triplet); D (doublet) SD TD S S S S S T T T S S D DD DD DD D

8 C4-C4- E A = eV (exp=3.882 eV Arnold et al 1991) B e = MHz ( exp B 0 = MHz; Zhao et al. 1996)  =0.0 Debyes 2108 (  g ), 1763 (  u ), 965(  g ),514 (π g ) ?, 255(π u ) ? X2gX2g 0.0 eV 1.4 eV 1.3 eV

9 C4C4C4C4 C4+C4+C4+C4+ C4-C4-C4-C4- C4HC4HC4HC4H C4H-C4H-C4H-C4H- C 3 Si isomers ?

10 d-C4 H.Masso, M.L.Senent, P. Rosmus, M.Hochlaf, J.Chem.Phys., 124, (2006), J.Chem.Phys., 124, (2006)

11 C4C4C4C4 C4+C4+C4+C4+ C4-C4-C4-C4- C4HC4HC4HC4H C4H-C4H-C4H-C4H- C 3 Si isomers ?

12

13 C4HC4H 0.0 eV 2.0 eV 1.0 eV X2+X2+22 Be= MHz  = Debyes E= 0.0 cm -1 Be= MHz  = Debyes E= 9 cm eV

14 C4H-C4H- B e = MHz (exp B0= Gupta el al 2007)  = Debyes (exp 6.2 Debyes, Agundez et al 2008) X1+X1+ 0.0 eV 3.0 eV2.6 eV 2.1 eV

15 C4H-C4H-

16 (R)CCSD(T)/aug-cc-pVQZ adiabatic electron affinities (eV) l-C 4 H + e - → l-C 4 H Exp=3.558 ± 0015 ( Taylor et al. (1998) r A -C 4 H + e - → r A -C 4 H r B -C 4 H + e - → r B -C 4 H d-C 4 H + e - → p-C 4 H p rA rB d l

17 Electronic States Dominant electron configuration E (eV) C 4 H - (X 1  + ) … (8  ) 2 (1  ) 4 (9  ) 2 (2  ) C 4 H - (1 3  ) … (8  ) 2 (1  ) 4 (9  ) 2 (2  ) 3 (10  ) C 4 H - (1 1  ) … (8  ) 2 (1  ) 4 (9  ) 2 (2  ) 3 (10  ) C4H-C4H- E A = 3.56

18 C4H-C4H- C 4 - +H The energy reference correspond to the lowest dissociation limit of the neutral C 4 H (C 4 (X 3  g - ) + H ( 2 S)). The 1 3  and 1 1  are correlating to the C 4 - (X 2 P g ) + H ( 2 S) dissociation limit. C4H-C4H- C4HC4H

19 Conclussions 1)Our calculations (E A and isomer relative energies) confirm the stabilization of linear carbon chains by electron attachment. 2)Our calculations confirm Barckholtz et al. (2001) predictions: C H mainly produces neutral C 4 H. The ISM formation process of C 4 H - remains unknown. 3)Bending mode frequencies of C 4 H - lye in the same region than the ones of many other carbon chains. This fact and the innacuracies of the theoretical and experimental techniques make difficult the identification by FIR techniques.


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