  CH$_3^+$, a cornerstone intermediate in interstellar chemistry, has recently
been detected for the first time by the James Webb Space Telescope. The
photodissociation of this ion is studied here. Accurate explicitly correlated
multi-reference configuration interaction {\it ab initio} calculations are
done, and full dimensional potential energy surfaces are developed for the
three lower electronic states, with a fundamental invariant neural network
method. The photodissociation cross section is calculated using a full
dimensional quantum wave packet method, in heliocentric Radau coordinates. The
wave packet is represented in angular and radial grids allowing to reduce the
number of points physically accessible, requiring to push up the spurious
states appearing when evaluating the angular kinetic terms, through a
projection technique. The photodissociation spectra, when employed in
astrochemical models to simulate the conditions of the Orion Bar, results in a
lesser destruction of CH$_3^+$ compared to that obtained when utilizing the
recommended values in the kinetic database for astrochemistry (KIDA).
