Surface Chemistry of Difluorovinylidene Species on Cu(111)
We investigated the reactivity of difluorovinylidene groups (C2F2) on Cu(111) under ultrahigh vacuum conditions. Difluorovinylidene moieties bonded to surface were generated by the dissociative adsorption of 1,1-dibromodifluoroethylene. Temperature Programmed desorption (TPD) and reflection-adsorption infrared spectroscopy (RAIRS) revealed the thermal reaction pathways, and a variety of intermediates were identified or inferred. The major desorption product, hexafluoro-2-butyne (C4F6), was detected at 445 K. It invokes a step of fluoride addition to difluorovinylidene to render the intermediacy of C2F3. However, differences exist when the vibration data from F + C=CF2 were compared with those from C?CF3 and CF=CF2 in previous literature, implying that the form is neither ethylidyne nor vinyl. Based on the concept of fluorine hyperconjugation, density function theory (DFT) calculations were utilized to obtain two transition states, quasi-vinyl and -ethylidyne, which can account for the differences present in the IR spectra. The relative thermal stability follows the trend of vinyl > quasi-ethylidyne > quasi-vinyl > vinylidene > ethylidyne suggested by IR and DFT calculations. Finally, the end product, CF3C¡ÝCCF3, might be formed by coupling of two quasi-ethylidyne species via the partial allenic forms.
Advisor:Yen-Nan Chiang; Chao-Ming Chiang; Hsiu-Wei Chen
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:rairs dft cu 111 difluorovinylidene uhv tpd
Date of Publication:07/25/2008