  Star formation quenching is one of the key processes that shape the evolution
of galaxies. In this study, we investigate the changes in molecular gas and
star formation properties as galaxies transit from the star-forming main
sequence to the passive regime. Our analysis reveals that as galaxies move away
from the main sequence towards the green valley the radial profile of specific
star formation rate surface density ($\Sigma_\mathrm{sSFR}$) is suppressed
compared with main sequence galaxies out to a galactocentric radius of 1.5
$R_{e}$ ($\sim$ 7 kpc for our sample). By combining radial profiles of gas
fraction ($f_\mathrm{gas}$) and star formation efficiency (SFE), we can discern
the underlying mechanism that determines $\Sigma_\mathrm{sSFR}$ at different
galactocentric radii. Analysis of relative contributions of $f_\mathrm{gas}$
and SFE to $\Sigma_\mathrm{sSFR}$ uncovers a diverse range of quenching modes.
Star formation in approximately half of our quenching galaxies is primarily
driven by a single mode (i.e. either $f_\mathrm{gas}$ or SFE), or a combination
of both. A collective analysis of all galaxies reveals that the reduction in
star formation within the central regions ($R$ $<$ 0.5 $R_{e}$) is primarily
attributable to a decrease in SFE. Conversely, in the disk regions ($R$ $>$ 0.5
$R_{e}$), both $f_\mathrm{gas}$ and SFE contribute to the suppression of star
formation. Our findings suggest that multiple quenching mechanisms may be at
play in our sample galaxies, and even within a single galaxy. We also compare
our observational outcomes with those from galaxy simulations and discuss the
implications of our data.
