  Given that the macromolecular building blocks of life were likely produced
photochemically in the presence of ultraviolet (UV) light, we identify some
general constraints on which stars produce sufficient UV for this
photochemistry. We estimate how much light is needed for the UV photochemistry
by experimentally measuring the rate constant for the UV chemistry (`light
chemistry', needed for prebiotic synthesis) versus the rate constants for the
bimolecular reactions that happen in the absence of the UV light (`dark
chemistry'). We make these measurements for representative photochemical
reactions involving SO$_3^{2-}$ and HS$^-$. By balancing the rates for the
light and dark chemistry, we delineate the "abiogenesis zones" around stars of
different stellar types based on whether their UV fluxes are sufficient for
building up this macromolecular prebiotic inventory. We find that the
SO$_3^{2-}$ 'light chemistry' is rapid enough to build up the prebiotic
inventory for stars hotter than K5 (4400 K). We show how the abiogenesis zone
overlaps with the liquid water habitable zone. Stars cooler than K5 may also
drive the formation of these building blocks if they are very active. The
HS$^-$ 'light chemistry' is too slow to work even for the Early Earth.
