High-resolution laser spectroscopy of the trans- and cis-1-vinylpropargyl radicals

Rotationally resolved spectra of the Ã2A′′–X̃2A′′ origin bands for both trans- and cis-conformers of 1-vinylpropargyl radical (1VPR) are experimentally studied. Rotational constants for both ground and electronically excited states are experimentally determined. The stability of the Ã2A′′ excited state of the cis-1VPR is found to be higher than that of trans-1VPR, which is likely due to additional π-overlap and increased pπ electron delocalization in the excited state of cis-1VPR.