Conformer lifetimes of ethyl cyanoformate from exchange-averaged rotational spectra.
Ethyl cyanoformate exists as a mixture of two conformers but displays three R-branch a-type band series in its rotational spectrum. Simulations with population fractions 0.37 at 210 K and 0.70 at 297 K undergoing conformer exchange with average conformer lifetimes, <tau(iso)>, shorter than approximately 40 ps at approximately 210 K and shorter than approximately 37 ps at 297 K reproduce the experimental spectra between 26.5 and 38 GHz, the exchanging species accounting for the third set of bands. The upper-limit <tau(iso)>'s are 1 order of magnitude longer than RRKM theory predictions and the population fractions are consistent with the total population with energy above 700 cm(-1), approximately twice the conformer interconversion barrier height. Model calculations indicate that extensive K-sublevel mixing in individual molecular eigenstates can produce the large population and the narrow distribution of the rotational-constant sum, B + C, consistent with the observed exchange-averaged band series.
True
Nancy S
NS
Department of Chemistry, University of California, Davis, Davis California 95616, USA.
D000097:Acetonitriles / Q000737:chemistry*; D005561:Formates / Q000737:chemistry*; D012399:Rotation; D013057:Spectrum Analysis / Q000379:methods*
D000097:Acetonitriles; D005561:Formates