J . A m . Chem. SOC.1989, 1 1 1 , 1185-1193 grants to R.T.O. and N.P.C.W. and a postdoctoral fellowship to R.T.B.
Registry No. 1 (R = H), 118436-74-1; 1 (R = CF,), 118436-72-9; 1 (R = CI), 118436-69-4; 1 (R = Ph), 118436-79-6; 1 (R = 4-MeOC6H4), 118436-80-9; 1 ( R = ~ - N O Z C ~ H 118436-78-5; ~), 2 (R = H), 11843673-0; 2 ( R = CF,), 118436-71-8; 2 (R = CI), 118436-67-2; 2 (R = F), 118436-68-3; 2 ( R = Br), 118436-66-1; 2 (R = Ph), 118436-77-4; 2 (R = CCI,), 118436-70-7; 2 (R = Bu-r), 118436-76-3; 2 (R = Me),
1185
118436-75-2; 3 (R = Ph), 94426-38-7; 3 (R = 4-MeOC6H4),11837776-7; 3 ( R = NO*C6H4), 118377-77-8; 3 (R = CI), 58589-34-7; 3 (R = CF,), 118377-78-9; 4 (R = F), 99344-85-1; 4 (R = CI), 85175-36-6; 4 (R = Br), 99344-91-9; 4 (R = Ph), 63481-05-0; 4 (R = CF,), 9384258-1; 4 (R = CCI,), 62635-18-1; 4 (R = Bu-r), 63432-63-3; 4 (R = Me), 82290-16-2; S,N,CI,, 5964-00-1; CFCI,, 75-69-4; 4-methoxybenzamidine, 22265-37-8; 4-nitrobenzamidine, 25412-75-3; N-(perfluoroacetimidoyl)perfluoroacetamidine,675-05-8; sulfur dichloride, 1054599-0.
Polymerization and Decomposition of Acetaldehyde on Ru( 00 1) M. A. Henderson, Y. Zhou, and J. M. White* Contribution from the Department of Chemistry, University of Texas, Austin, Texas 78712 Received July 8, I988
Abstract: The polymerization and decomposition of acetaldehyde (CH3CHO) on Ru(001) was studied by high-resolution electron energy loss spectroscopy (HREELS), static secondary ion mass spectrometry (SSIMS), and temperature-programmed desorption (TPD). Evidence is presented that low exposures (1 langmuir. For CH,CHO exposures above about I langmuir, desorption of multilayer CH,CHO occurs at 150 K (Figure 2). in agreement with previous studies.',% The multilayer state is evidenced in HREELS by lmes at 2780, 2275, 1715, 790, and 126 cm-' (Figures 8c and l o a ) assigned to "(CH), [6(CH,) p(CHI)]. v(CO), 6(CH), and solid acetaldehyde lattice vibration, respecti~ely.'.'~,'~The ",(CHI), 6,(CHl), and p(CHl) losses cannot be differentiated from those of the polymer (to be discussed). The formation of the multilayer in HREELS coincides roughly with the C H I C H O exposure that saturates the H, (and CO) TPD (Figure I).Also, the +SSIMS ion yield ratios for C H O f / R u ' , C H I C O + / R u + . and (CH,CHO)H+/Ru+ all increase for C H I C H O exposures above 0.6 langmuir and are attributable to growth of the multilayer state. (Figure 5 ) . 4.1.4. Polymerization above the Surface, >1.5 Iangmuir. Although exposures of C H I C H O above 1.0 langmuir result in multilayer formation, a new species also develops that we attribute to three-dimensionalpolymerization above the surface. The large desorption slate at 250 K develop only after the H, TPD saturates
+
(26) Shanahan,
K. L.; Mucttcrics. E. L. J . Phyr. Chcm. 1984.88, 1996.
1192 J. Am. Chem. SOC..Vol. 111. No. 4, 1989
and after the multilayer appears and is attributable to decomposition of this polymerized CH3CH0. Assuming a relatively constant sticking coefficient at I I O K. the amount of CH,CHO still adsorbed after heating 25 langmuir above 150 K is far greater than what can be accommodated in the first surface layer. Polymerization above the surface is a suitable explanation for both the stability and quantity remaining. It is also significant that +SSIMS ions involving multimers of CH,CHO are observed only for exposures >1.0 langmuir (Figures 4 and 5). These ions are not due to simple multilayer CH,CHO since annealing above I50 K does not remove them from +SSIMS (Figures 6 and 7). Additional evidence for polymerization above the surface at high CH,CHO exposures is given by HREELS. Table Ill wmpares the HREEL losses of 25-langmuir CH,CHO, CHICDO, and CD,CDO heated to 150 K with the IR peaks of crystalline polyacetaldehyde catalyzed with a metal alkoxide." There is g d agreement between our HREELS data and the IR data for the crystalline polymer. CH,CHO polymerization in hydrocarbon solutions&'* requires low temperatures (
