Nicholas R. Walker, Susanna L. Stephens, David P. Tew and Anthony C. Legon 1 68 th International Symposium on Molecular Spectroscopy, Ohio State University, Unexpected Generation and Observation of a T-shaped Complex of C 2 H 2  AgCCH Engineering and Physical Sciences Research Council

M  CCH Complexes - A Recent History AlCCH – M. Sun, D.T. Halfen, J. Min, D.J. Clouthier, L.M. Ziurys, Chem. Phys. Lett. 553, (2012). ZnCCH – J. Min, D.T. Halfen, M. Sun, B. Harris, L.M. Ziurys, J. Chem. Phys. 136, (2012). LiCCH, NaCCH, KCCH – P.M. Sheridan, M.K.L. Binns, M. Sun, J. Min, M.P. Bucchino, D.T. Halfen, L.M. Ziurys, J. Mol. Spectrosc. 269, (2011) CuCCH – M. Sun, D.T. Halfen, J. Min, B. Harris, D.J. Clouthier, L.M. Ziurys, J. Chem. Phys. 133, (2010). AlCCH, AgCCH – C. Cabezas, S. Mata, A.M. Daly, A. Martin, J.L. Alonso, J. Cernicharo, J. Mol. Spectrosc. 278, (2012)

water hydrogen sulphide ethene acetylene ammonia What is the nature of the interaction between each of these molecules and a single metal atom in isolation? MH09, 67 th International Symposium on Molecular Spectroscopy, Ohio State University, 2012.

Power divider SPST switch Mixer Low noise amplifier Pin diode limiter Adjustable attenuator 300 W Power amplifier AWG ( GHz) Oscilloscope (0-12 GHz) 10 MHz reference frequency PDRO (19.00 GHz) GHz GHz 12.2 GHz Low-pass band filter CP-FTMW Spectrometer

Laser ablation source informed by the designs currently used by Legon and co-workers, Duncan and co-workers, Gerry and co-workers, Ziurys and co-workers. Laser ablation source

C 2 H 2  AgF ??? Frequency / MHz Frequency / MHz Frequency/MHz K -1 = 0 K -1 = 1 Two spectra almost overlapped. Silver isotopes ! J   J = 4  5

C 2 H 2  AgF Discover rotational constants are much too small to correspond to C 2 H 2  AgF in any physically-reasonable geometry. But evidence says complex must be T-shaped, contain C 2 H 2 and a silver atom very close to the centre of mass. C 2 H 2  AgCCH This would require a degree of C 2 H 2 fragmentation within the laser ablation source but also involve formation of a complex. We did not expect to see M-CCH complexes. Do we have AgCCH in the spectrum?

Frequency / MHz Yes! J   J = 1  2 AgCCH

12 C 2 H 2  107 Ag 12 C 12 CH 12 C 2 H 2  109 Ag 12 C 12 CH A 0 / MHz 34936(50)34953(120) B 0 / MHz (26) (61) C 0 / MHz (26) (60)  J / kHz (39)0.1714(92)  JK / kHz 23.86(28)23.58(67) N 14  / kHz C 2 H 2  107 Ag 13 C 13 CH 13 C 2 H 2  109 Ag 13 C 13 CH A 0 / MHz 33239(41)32347(433) B 0 / MHz (91) (12) C 0 / MHz (95) (12)  J / kHz (43)0.117(43)  JK / kHz 20.38(17)22.8(18) N 67  / kHz

A 0 / MHz  0 / u Å 2 r(Ag  *) / Å 12 C 2 H 2  107 Ag 12 C 12 CH 34936(50)0.34(3)2.2404(5) 12 C 2 H 2  107 AgCl 34904(45)0.34(4)2.1841(82) B 0 / MHz C2H2C2H (54)-- Ag-C 1 bond distance in AgCCH optimised through measurements of transitions of Ag 12 C 12 CH, Ag 13 C 13 CH. C1C1 C2C2 H Ag C2H2C2H2 Molecular Geometry of C 2 H 2  AgCCH * (1) S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker and A.C. Legon, J. Chem. Phys (2012) (2) M. Herman, A. Campargue, M.l. El Idrissi and J. Vander Auwera, J. Phys. Chem. Ref. Data, 32, 921 (2003).

Conclusions A new complex of C 2 H 2 and AgCCH has been observed. The molecular geometry is T-shaped and planar. The intensities of transitions of this species and also free AgCCH are enhanced by the presence of SF 6 in the gas sample! This raises lots of interesting questions about “synthetic” routes to complexes generated through laser ablation. Not yet identified transitions of C 2 H 2  AgF despite using a broadband spectrometer to search for them. Have previously noticed that some combinations of B and MX are very difficult to observe. For example, H 2 S  AgF.

Acknowledgements David Tew (Bristol) Susanna Stephens (Bristol) Anthony C. Legon (Bristol) Financial Support Engineering and Physical Sciences Research Council Bristol In transit Newcastle