15min:

DILRUKSHI HEWAGE, MOURAD ROUDJANE AND DONG-SHENG YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

C-H bond activation of small hydrocarbons is of importance in chemistry and industrial applications. La(C₃H₂) was formed by the reaction of laser-ablated La atoms and propyne (C₃H₄) in supersonic molecular beams. Two isomers of La(C₃H₂) were detected for the first time by mass-analyzed threshold ionization (MATI) spectroscopy. From the MATI spectra, the two isomers exhibit origin bands at 42953(5) and 43609(5) cm^-1 and vibrational intervals of 425 and 535 cm^-1, respectively. They were identified as La(CCCH₂) formed from 1,3-dehydrogantion and La(HCCCH) formed by 3,3-dehydrogenation and were confirmed by measurements with deuterium substituted propyne (C₃D₄) as the precursor. The 1,3-dehydrogenated complex shows a higher ionization energy and larger metal-ligand stretching frequencies than the 3,3-dehydrogenated species. Based on DFT/B3LYP calculations, the electronic transitions responsible for the observed MATI spectrum of La(HCCCH)isomer is ¹A ²A,and that of La(CCCH₂)isomer is ¹A' ²A'.