Gauche-Trans Conformational Changes in Ethyl Formate Chemisorbed on Ni(111): Coverage-Dependent RAIRS Spectra

Abstract

Infrared reflectance spectra of ethyl formate on Ni(111) at 105 K were recorded as a function of surface coverage. The RAIRS activities of several bands are found to vary in a correlated manner as a function of coverage. The activity of both the asymmetric stretching vibration and the twisting vibration of the CH2 group at low coverages conclusively show that adsorption occurs initially in the s-cis,gauche conformation. These two bands fade out on increasing the coverage and are completely removed at full monolayer coverage. The coverage dependence is interpreted in terms of rotational isomerization to a planar conformation as the packing density in the adlayer is increased. The results are consistent with an attribution of the full coverage molecular structure to the s-trans,trans conformation.

Thermal Processing and Interactions of Ethyl Formate in Model Astrophysical Ices Containing Water and Ethanol

“…The top spectrum (A) in Figure 5 shows the RAIR spectrum of 100 L m ethyl formate adsorbed on HOPG at 30 K. At 30 K, the same bands were observed for all exposures investigated and hence the 100 L m spectrum is shown as it has a good signal to noise ratio. The RAIR spectrum shown in Figure 5A is in good agreement with that seen previously for the formation of multilayer ethyl formate on Ni(111) [19][20][21][22] . The assignments for the infrared bands shown in Figure 5 are made by comparison to the literature 14,[19][20][21][22]53 and are shown in Table 2.…”

“…The desorption temperature of the multilayer observed in Figure 2 is in good agreement with that observed for the desorption of multilayer ethyl formate from a Ni(111) surface 19,21 . TPD data for ethyl formate adsorbed on Ni(111) also showed thermal decomposition in the TPD at higher temperatures [19][20][21][22] . However, there is no evidence for decomposition in our TPD data, which is unsurprising given that the desorption temperature suggests that the molecule is physisorbed on the HOPG surface.…”

“…As the exposure is increased, a mixture of different conformations is observed, but at full monolayer coverages, the conformation changes to s-trans, trans. This conformation allows a more closely packed adlayer to form on the surface 20 . This is also the conformation that has been most abundantly observed in star-forming regions 10 .…”

Comparison of surface structures of poly(ethyl methacrylate) and poly(ethyl acrylate) in different chemical environments

“…31 The sps spectrum is dominated by the asymmetric stretch of the side chain methyl group at 2975 cm À1 . 31,37 The SFG spectra collected from PEA are very similar to those of PEMA, indicating that the surface of PEA is also covered by the ester ethyl side chains. Similarly, the vibrational peaks at 2935/2870, 2970, and 2900 cm À1 in the SFG spectra of PEA are assigned to the symmetric/Fermi resonance and asymmetric stretches of the methyl groups at the side chain end, and the symmetric stretch of methylene groups on the side chains, respectively.…”

“…Extensive research has been performed to assign C-H stretching peaks for similar ester ethyl groups in simple compounds such as ethyl formate and ethyl acetate. [31][32][33][34][35][36][37][38] Unfortunately, conflicting assignments exist in many of these publications. We adopted the assignment results from an early article, in which the authors assign the C-H stretching peaks for ester ethyl groups of ethyl acetate in infrared spectra by selectively deuterating each methylene group, methyl group, or combination of methyl and methylene groups alternatively.…”