Infrared Spectroscopy of H + (C 2 H 2 ) n Ar and H + (C 2 H 4 ) n Ar (n=1,2) Gary E. Douberly, Allen M. Ricks, Brian W. Ticknor, and Michael A. Duncan Department of Chemsitry University of Georgia Funding: National Science Foundation

Non-Classical Non-Classical Classical Vinyl cation A. R. Sharma, J. Wu, B. J. Braams, S. Carter, R. Schneider, B. Shepler, and J. M. Bowman, J. Chem. Phys 125, (2006) Plasma Chemistry, Astrophysics, Quantum Chemistry, Spectroscopy T. Oka (1989, 1995) High Resolution Spectroscopy of  6 (asymmetric CH stretch) Bridged, Non-Classical, Carbonium ion Prototype of Carbonium ions, Reaction Intermediates in Organic Chemistry Protonated Acetylene

Experiment Pulsed Discharge Cluster Source

to ~ n= psi 1:10:20:100 C 2 H 2 : H 2 : Ar : (70/30) Ne/He 39 Ne +

OPO OPA 1 crystal angle tuned 4 crystals angle tuned signal (not used) idler 532 nm 1064 nm KTP oscillator KTA diff. gen. + amp of idler beam LiInS 2 diff. gen. Tunable  m 2 crystals angle tuned Tunable mid-IR  m 900 V 750 ns LaserVision (Dean Guyer)

MP2 / aug-cc-pVTZ H + (C 2 H 2 )-Ar Proton stretch

C 4 H 5 + (C 2 H 2 ) H + (C 2 H 2 ) 3

? D e (Ar) ~1200 cm -1 Protonated Ethylene

Protonated Ethylene Dimer ? t-butyl cation !

Summary Confirmation of Non-Classical Bridged Structure of Protonated Acetylene First observation of Proton Stretch  2 in H + (C 2 H 2 )-Ar 900 cm -1 red-shift of Proton Stretch upon formation of Bridged Dimer Higher order clusters consist of 4 membered ring C 4 H 5 + (C 2 H 2 ) n Formation of various Carbocations in acetylene discharge! Infrared Spectroscopy of mass-selected Carbocations! C + (CH 3 ) 3 t-butyl cation