FTIR AND DFT STUDIES OF THE MgC 3 - ANION IN SOLID Ar M. Bejjani, C. M. L. Rittby, and W. R. M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX th International Symposium on Molecular Spectroscopy The Ohio State University June 20-24,

Objectives  Synthesize small novel metal carbide molecules  Determine the vibrational fundamentals and molecular structure based on the infrared spectrum of the molecule  13 C isotopic shift measurements  Density Functional Theory (DFT) 2 Motivation  Application to astrophysics  Application to materials science (e.g. metcars)

Astrophysics 2 atoms3 atoms4 atoms5 atoms6 atoms7 atoms8 atoms9 atoms H2H2 C3C3 c-C 3 HC5C5 C5HC5HC6HC6HCH 3 C 3 NCH 3 C 4 H AlFC2HC2Hl-C 3 HC4HC4Hl-H 2 C 4 CH 2 CHCNHCOOCH 3 CH 3 CH 2 CN AlClC2OC2OC3NC3NC 4 SiC2H4C2H4 CH 3 C 2 HCH 3 COOH(CH 3 ) 2 O CN - C2SC2SC3OC3Ol-C 3 H 2 CH 3 CNHC 5 NC7HC7HCH 3 CH 2 OH C2C2 CH 2 C3SC3Sc-C 3 H 2 CH 3 NCCH 3 CHOH2C6H2C6 HC 7 N CH, CH + HCNC2H2C2H2 H 2 CCNCH 3 OHCH 3 NH 2 CH 2 OHCHOC8HC8H CNHCO, HCO + NH 3 CH 4 CH 3 SHc-C 2 H 4 Ol-HC 6 H ?CH 3 C(O)NH 2 CO, CO + HCS + HCCNHC 3 NHC 3 NH + H 2 CCHOHCH 2 CHCHO ?C8H–C8H– CPHOC + HCNH + HC 2 NCHC 2 CHOC6H–C6H– CH 2 CCHCNC3H6C3H6 SiCH 2 O, H 2 O + HNCOHCOOHNH 2 CHOH 2 NCH 2 CN HClH2SH2SHNCSH 2 CNHC5NC5N KClHNCHOCO + H2C2OH2C2Ol-HC 4 H ? NHHNOH 2 COH 2 NCNl-HC 4 N NOMgCNH 2 CNHNC 3 c-H 2 C 3 O NSMgNCH 2 CSSiH 4 H 2 CCNH ? NaClN2H+N2H+ H3O+H3O+ H 2 COH + C5N–C5N– OHN2ON2Oc-SiC 3 C4H–C4H– PNNaCNCH 3 HC(O)CN SO, SO + OCSHOCN SiNSO 2 HSCN SiOc-SiC 2 C3N–C3N– CH 3 C 5 NHC 9 NC 6 H 6 ?HC 11 N SiSCO 2 PH 3 ?(CH 3 ) 2 COCH 3 C 6 HC 2 H 5 OCH 3 ?C 60 CSNH 2 HCNO(CH 2 OH) 2 C 2 H 5 OCHOn-C 3 H 7 CNC 70 HFH3+H3+ CH 3 CH 2 CHO SH + H2D+H2D+ HDHD 2 + FeO ?SiCN O 2 ?AlNC CF + SiNC SiH ?HCP POCCP AlOAlOH OH + KCN H 2 Cl + 10 atoms11 atoms12 atoms> 12 atoms Source: Cologne Database for Molecular Spectroscopy, April

Materials science  Small metal-carbide molecules may help in understanding the bonding and the growth mechanism of larger clusters such as metallocarbohedrenes (metcars).  Large MC 2 production indicates MC 2 may serve as a fundamental building block of larger metcar clusters (M 8 C 12 ). M C C 4

Previous work on MgC n clusters (n>2)  No experimental observations of any MgC n clusters have so far been reported.  Theoretical studies (Largo et al., 2001 and 2003)  MgC n (n=2-7)  n-even: cyclic isomers preferred  n-odd: chain preferred  MgC n +, MgC n - (n=2-7)  Chains except for MgC 2 +, MgC 2 - and MgC 3 + 5

2 A 1 rhombic C1C1 C3C3 Mg C2C Σ linear Mg C1C1 C2C2 C3C MgC 3 + cation MgC 3 neutral, anion and cation (Largo et al.) C3C3 C2C2 C1C1 Mg 2 A'' bent ° 174.8° Mg C1C1 C2C2 C3C3 4 Σ linear C1C1 C3C3 Mg C2C A 1 rhombic 2.3 MgC2C2 C3C3 C1C B 1 fan MgC 3 - anion Π linear Mg C1C1 C2C2 C3C A 1 rhombic C1C1 C3C3 Mg C2C C3C3 C2C2 C1C ° Mg 1 A' bent ° C1C1 C3C3 Mg C2C2 1 A 1 rhombic B 2 fan 1.3 MgC2C2 C3C3 C1C B 2 ring MgC1C1 C2C2 C3C ° MgC 3 neutral

Nd-YAG 1064 nm pulsed laser Quartz window Laser focusing lens Ar To pump Torr or < CsI window To pump Torr Carbon rod Magnesium rod Gold mirror ~ 12 K Bomem DA3.16 Fourier Transform Spectrometer KBr beam splitter liquid N 2 cooled MCT detector ( cm -1 ) 0.2 cm -1 resolution Experimental apparatus 7

Candidates for Mg n C m bands C n ? ● C6C6 ●● (a) 12 C rod (b) 12 C rod + Mg rod Absorbance Mg n C m ? C7-C ● ● ● ● Frequency (cm -1 ) ●

SpeciesB3LYP/6-311+G(d) MgC 3 ( 3 Π) (1.8), (0.3), (2.9), (98.6), (10.0), (135.7), (101.0) MgC 3 ( 1 A′) (3.4), (5.3), (6.5), (30.0), (27.7), (764.6) MgC 3 + ( 2 Σ) (16.2), (0.0), (24.8), (50.4), (14.8), (827.8) MgC 3 - ( 2 A′′) (8.5), (63.4), (22.6), (16.1), (217.4), (922.9) MgC 3 - ( 4 Σ) (0.2), (43.7), (27.4), (0.7), (20.2) DFT calculations: vibrational frequencies (cm -1 ) and intensities (km/mol) for open-chain MgC 3 species Experimental1190.1, cm -1

Effects of 20% 13 C isotopic substitution x CnCn x x x x (b) 22 K Absorbance Frequency (cm -1 ) (a) 12 K x x x x Mg n 12 C m ? 10

MgC 3 ( 3 Π)MgC 3 - ( 2 A′′)MgC 3 - ( 4 Σ) Isotopomer Mg-C-C-C Observed ν Scaled ν Difference Δ ν Scaled ν Difference Δ ν Scaled ν Difference Δν Mg ……………… Mg Mg Mg Mg Mg Mg Mg Observed vs theoretical 13 C isotopic shifts 11 Std deviation= 4.1Std deviation= 2.7Std deviation= 0.4

 Linear MgC 3 - anion has been observed in its 4 Σ ground state.  Its ν 1 (σ) vibrational fundamental is identified at cm -1.  The cm -1 band may be the ν 2 (σ) mode. Mg Conclusions 12 Frequency (cm -1 ) x x x x x x x x Absorbance MgC 3 - ( 4 Σ) (0.7), (20.2)

13 Acknowledgments  The Welch Foundation  TCU Research and Creative Activities Fund  The Graduate Student Travel Grant Program  W. M. Keck Foundation for the Bomem spectrometer

14 References 1 P. Redondo, C. Barrientos, and A. Largo, Chemical Physics Letters 335, 64 (2001). 2 P. Redondo, C. Barrientos, A. Climas, and A. Largo, J. Phys. Chem. A 107, 4676 (2003). 3 P. Redondo, C. Barrientos, A. Climas, and A. Largo, J. Phys. Chem. A 107, 6317 (2003).