Photolysis of geminal diiodoalkanes in the presence of molecular oxygen has become an established
route to the laboratory production of several Criegee intermediates, and such compounds also have
marine sources. Here, we explore the role that the trihaloalkane, chlorodiiodomethane (CHI2Cl), may
play as a photolytic precursor for the chlorinated Criegee intermediate ClCHOO. CHI2Cl has been
synthesized and its UV absorption spectrum measured; relative to that of CH2I2 the spectrum is
shifted to longer wavelength and the photolysis lifetime is calculated to be less than two minutes.
The photodissociation dynamics have been investigated using DC slice imaging, probing ground state
I and spin-orbit excited I* atoms with 2+1 REMPI and single-photon VUV ionization. Total
translational energy distributions are bimodal for I atoms and unimodal for I*, with around 72% of
the available energy partitioned in to the internal degrees of freedom of the CHICl radical product,
independent of photolysis wavelength. A bond dissociation energy of D0 = 1.73±0.11 eV is inferred
from the wavelength dependence of the translational energy release, which is slightly weaker than
typical C–I bonds. Analysis of the photofragment angular distributions indicate dissociation is
prompt and occurs primarily via transitions to states of A″ symmetry. Complementary high-level
MRCI calculations, including spin-orbit coupling, have been performed to characterize the excited
states and confirm that states of A″ symmetry with highly mixed singlet and triplet character are
predominantly responsible for the absorption spectrum. Transient absorption spectroscopy has
been used to measure the absorption spectrum of ClCHOO produced from the reaction of CHICl with
O2 over the range 345–440 nm. The absorption spectrum, tentatively assigned to the syn conformer,
is at shorter wavelengths relative to that of CH2OO and shows far weaker vibrational structure.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)