Constraining the Conformational Landscape of a Polyether Building Block by Raman Jet Spectroscopy

Abstract

Collisionally induced chain isomerization of CH3OCH2CH2OCH3 around its three central torsional angles is characterized in a supersonic slit jet by probing compound-seeded carrier gas expansions with focussed 5-25 W cw 532 nm radiation as a function of carrier gas, nozzle temperature and distance. Spontaneously Raman scattered photons are collected and dispersed down to 100 cm(-1). They reveal important contributions from three chain conformations in the expansion. Isomerization around the outer torsional angle is found to be feasible, whereas the central OCCO angle remains largely conserved under most expansion conditions. The spectroscopic results are used for a critical assessment of quantum-chemical predictions for the energy sequence of the three low-lying conformations. The stretched global minimum energy structure of this polyether building block is consistent with a statistical model of the dominant unimolecular relaxation pathways.