Fumie X. Sunahori, Jie Wei, and Dennis J. Clouthier Department of Chemistry, University of Kentucky

HCP + ?? Previously…

HCP + CCP !! v ' =0 Discovery

Why Study CCP?  No previous work  Only 8 of 44 possible dicarbides have been discovered (C 2 X, X = H, B, C, N, O, Si, S, Cl)  Structure (Linear? Cyclic?)  Astrophysical Significance

Experimental Gas Mixture: CH 4 + PCl 3 in Ar

HCP + CCP Are We Sure? ??

88 66 77 22 33 X 2  r  99 (1) 2  Excited state (2) 2  - Excited state (3) 2  + Excited state Background

[core] 6  2 7  2 8  2 2  4 9  2 3  1  X 2  r Split the ground state into two spin-components A  2  1/2 2  3/2 E Excited State If It Is CCP…

A = cm -1 HCP + |A|= cm -1 Low-Resolution LIF Spectrum

1.Rotational Constant B"(CCP) = cm -1 [exp. B" = cm -1 ] B"(CPC) = cm -1 2.Spin-Orbit Coupling Constant Small A is expected for CPC cf. A"(CCN) = cm -1  A"(CNC) = cm -1 3.Stability CPC is predicted to lie much higher (88.0 kcal) a in energy compared to the ground state CCP 4.Number of isotopomers 3 isotopomers for CPC; 4 isotopomers for CCP a CCSD(T)/cc-pVTZ calculation; J. El-Yazal et al. J. Phys. Chem. A. 101, 8319(1997). Can It be CPC?

Exp. 1 = 1644 cm -1 3 = 833 cm -1 A = 142 cm -1 Exp. 1 = 1594 cm -1 3 = 813 cm -1 A = 145 cm -1 A A Vibrational Structure Ab initio 1 = 1726 cm -1 3 = 847 cm -1 Ab initio 1 = 1659 cm -1 3 = 829 cm -1

1 = 1644 cm -1 3 = 833 cm -1 A = 142 cm -1 Exp. 1 = 1692 cm -1 3 = 661 cm -1 A = 874 cm -1 Discovery of CCAs Ab initio 1 = 1749 cm -1 3 = 675 cm -1

CH 4 + PCl 3 13 CH 4 + PCl cm -1 [37.8 cm -1 ] 41.0 cm -1 [41.8 cm -1 ] 75.5 cm -1 [81.2 cm -1 ] Isotope Shifts 12 CH CH 4 + PCl 3

Rotational Analysis A' cm -1

Spin-Orbit Coupling Constant A X 2rX 2r ~ A 2iA 2i ~ A" cm -1 A' cm -1 A' (CCN) -0.8 cm -1 A" (CCN) cm -1 R 11 (1.5) R 21 (1.5) 22 22    

[ Å] Å [ Å] Å 1: CCSD(T) calculations Å Å Å Å [ Å] 1 Structure of CCP (X 2  ) ~

1.673 Å 1: B3LYP calculations Å Å [ Å] Å [1.698 Å] 1 Structure of CCP (A 2  ) ~

Effective Hamiltonian: H = H vib + H SO + H RT + H a + H FR  =  2 = cm -1 A  = cm -1 Renner-Teller Analysis (X 2  ) ~

Renner-Teller Analysis (A 2  ) Effective Hamiltonian a H = H vib + H RT + H a + H SO ~   24g 4 ^ 4g K a J. M. Brown & F. Jørgensen, Mol. Phys. 47, 1065 (1982).

CCP in Space FD07 “Detection of the CCP Free Radical in IRC+10216” D. T. Halfen, D. J. Clouthier, and L. M. Ziurys

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Renner-Teller Anaysis (A 2  ) (Energy Formulae) For Unique Levels (|K|  v 2 ): For Non-Unique Levels (|K| < v 2 ): where

Constants X 2  A 2A 2 B"B" (52)B'B' (51) A"A" (42)A'A' (36) 10 4 A D " (31)T0T (21)

12 C 2 P 13 C 2 P 1 (58) (27) 2 (91)204.01(96) 3 (44)819.0(15) gKgK (11) (13)  (62) (61) A (10) (10) Renner-Teller Analysis (X 2  ) ~

Renner-Teller Analysis (A 2  ) ~ 12 C 2 P 13 C 2 P 1 (15) (78) 2 (14)294.58(29) 3 (17)714.13(64) gKgK 1.62(31) (11) g (4) (10) g4g4 0.62(5)0.566(24) ^

1 =1 2 =1 1 =-1 2 =-1  = 2  = -2  1 =-1 2 =1 1 =1 2 =-1  = 0  2+2+4-4- 22 2-2-