posted on 2019-04-04, 00:00authored byPeter
R. Franke, Joseph T. Brice, Christopher P. Moradi, Henry F. Schaefer, Gary E. Douberly
Helium-solvated ethylperoxy
radicals (CH3CH2OO•) are formed
via the in situ reaction between 2A′ ethyl radical
and 3Σg– dioxygen. The
reactants are captured sequentially
through the droplet pick-up technique. Helium droplets are doped with
ethyl radical via pyrolysis of di-tert-amyl peroxide
or n-propylnitrite in an effusive, low-pressure source.
An infrared spectrum of ethylperoxy, in the CH stretching region,
is recorded with species-selective droplet beam depletion spectroscopy.
Spectral assignments are made via comparisons to second-order vibrational
perturbation theory with resonances (VPT2 + K) based on coupled-cluster
full quartic force fields. Cubic and quartic force constants, evaluated
using a small basis set, are transformed into the normal coordinate
system of the higher level quadratic force constants. This transformation
procedure eliminates the mismatch between normal modes, which is a
source of error whenever normal coordinate force constants from different
levels of theory are combined. The spectrum shows signatures of both
the C1gauche and Cstrans rotamers
in an approximate 2:1 ratio; this is despite the prediction that the gauche rotamer lies 44 cm–1 lower on the
zero-Kelvin enthalpic potential surface for torsional interconversion.
Helium droplets are 0.4 K at equilibrium; therefore, in situ ethylperoxy
production is highly nonthermal.