  The reaction dynamics of H$_2$COO to form linear HCOOH and dioxirane as first
steps for OH-elimination is quantitatively investigated. Using a machine
learned potential energy surface at the CASPT2/aug-cc-pVTZ level of theory
vibrational excitation along the CH-normal mode $\nu_{\rm CH}$ with energies up
to 40.0 kcal/mol ($\sim 5 \nu_{\rm CH}$) leads almost exclusively to linear
HCOOH which further decomposes into OH+HCO. Although the barrier to form
dioxirane is only 21.4 kcal/mol the reaction probability to form dioxirane is
two orders of magnitude lower if the CH-stretch mode is excited. Following the
dioxirane-formation pathway is facile, however, if in addition the COO-bend
vibration is excited with energies equivalent to $\sim (2 \nu_{\rm CH} + 4
\nu_{\rm COO})$ or $\sim (3 \nu_{\rm CH} + \nu_{\rm COO})$. For OH-formation in
the atmosphere the pathway through linear HCOOH is probably most relevant
because the alternative pathways (through dioxirane or formic acid) involve
several intermediates that can de-excite through collisions, relax {\it via}
Intramolecular vibrational energy redistribution (IVR), or pass through very
loose and vulnerable transition states (formic acid). This work demonstrates
how, by selectively exciting particular vibrational modes, it is possible to
dial into desired reaction channels with a high degree of specificity for a
process relevant to atmospheric chemistry.
