JET-COOLED $\tilde{A}$-$\tilde{X}$ SPECTRA OF THE $\beta$-HYDROXYETHYLPEROXY and $\beta$-HYDROXYETHYLPEROXY-OD RADICALS

Abstract

The $\beta$-hydroxyethylperoxy (HOCH$_2$CH$_2$OO, $\beta$-HEP) radical in the atmosphere arises from the reaction of ethene (CH$_2$CH$_2$) and hydroxyl radical (OH), followed by the reaction with oxygen (O$_2$). It is also an important intermediate in the oxidation of ethanol, a component of automotive fuel. High-resolution, jet-cooled cavity ring-down spectroscopy (resolution of $\Delta\nu\approx$250MHz, considering the instrumental linewidth and the residual Doppler broadening) has been applied to observe the $\tilde{A}$-$\tilde{X}$ origin band of the most stable conformer of both $\beta$-HEP and mono-deuterated $\beta$-HEP (DOCH$_2$CH$_2$OO, $\beta$-HEP-OD). Broadened rotational contours are observed for both isotopologues, but more resolved structure is shown in the $\beta$-HEP-OD spectrum. The evolutionary algorithm approach is applied to analyze the spectra, which gives fitted rotational constants and the homogeneous linewidths for both isotopologues using an asymmetric-top model for the rotational Hamiltonian. Evidence corresponding to a narrower homogeneous linewidth in the $\beta$-HEP-OD spectra implies that the broad rotational contour of $\beta$-HEP likely involves the motion of the hydrogen of the OH group.