Mass-Correlated High-Resolution Spectra and the Structure of Benzene

Mass-correlated rotational alignment spectroscopy resolved
the
rotational Raman spectra for 5 benzene isotopologues with unprecedented
resolution. 13-C isotopologues were characterized at natural abundance.
Fitted rotational constants allowed the analysis of effective and
equilibrium bond lengths for benzene with sub-mÅ uncertainties.
We found that previously reported experimental structures were wrong
by multiple mÅ, due to unrecognized H/D isotope effects. Our
results also refute recent experimental and theoretical literature
claims of identical effective C–H and C–D bond lengths
in benzene and reveal an isotope effect similar to that in other small
molecules.