Pretty sure it's not in the module, but my research tells me it is a spell at level 8 for clerics with that domain.
NWN domains, even with our custom spells adding some extras, do not have all the spells granted by PnP domains, which give a new spell at every spell level (but it can only be cast once a day - you only get one slot to cast one domain spell per level, period [chosen from the options granted by your two domains - so you'll have to pick one of the two each day, and cannot use the other that day], unlike NWN's ability to just memorize them normally).
Sun Domain currently grants the following extra spells on CD: Sunscorch (1), Searing Light (2), Sol's Searing Orb (5), Sunbeam (7). This list is not likely to be altered or expanded.