Conformational stability of 1-butene: an electron momentum spectroscopy investigation.

The valence-shell electron momentum distributions for 1-butene are measured by electron momentum spectroscopy (EMS) employing non-coplanar symmetric geometry. The experimental electron momentum distributions are compared with the density functional theory (DFT) calculations using different-sized basis sets. Although the two conformers of 1-butene in the gas phase, namely the skew and syn, have very close ionization potentials, the electron momentum distributions, especially in the low momentum region, can show prominent differences for some of the valence orbitals. By comparing the experimental electron momentum profiles with the theoretical ones, the skew conformer is found to be more stable than the syn and their relative abundances at room temperature are estimated to be (69 +/- 6)% and (31 +/- 6)%, respectively. It demonstrates that EMS has the latent potential to study the relative stability of conformers.