  We study the formation of C$_{18}$H and C$_{18}$H$_2$ by irradiating a
cyclo[$18$]carbon molecule with atomic and molecular hydrogen at impact energy,
$E$, in the range of 0.5-25 eV. We utilize the density-functional tight-binding
method to perform molecular dynamics simulations to emulate the interaction of
a carbon ring when colliding with atomic or molecular hydrogen. From our
results, the formation of the C$_{18}$H molecules is likely to occur upon
irradiating by H atoms at $E < 10$ eV and by H$_2$ molecules at $2 < E < 15$ eV
center of mass energy. Formation of C$_{18}$H$_2$ molecules is only observed at
around $E = 2$ eV. Our results show that the absorption of hydrogen is more
prone in atomic than in molecular hydrogen atmosphere. Thus, we find that the
probability of physio-absorption reaches up to 80 \% for atomic projectiles
with $E < 5$ eV but only up to 10 \% for the molecular ones. Our analysis shows
that the deformation of the carbon ring due to the hydrogen bonding produces
transition from $sp$ to $sp^2$ hybridization. The angle between the carbon
atoms at the locations near to the H bond in the resulting ring is not 120$^o$
but instead 110$^o$ degrees. No molecular fragmentation of the C$_{18}$ ring is
observed.
