Two key parameters are the temperature and duration (or residence time), which are adjusted to optimize yield, conversion, and avoidance of intractable products.
[1] Often the experiment entails volatilizing a precursor, which is drawn through a "hot zone" followed by rapid condensation.
The hot zone must impart heat to the gaseous molecules, so it is generally packed with solids to induce gas-solid collisions.
Rapid post-reaction cooling and the dilution inherent in gases both suppress bimolecular degradation pathways.
[4] The strained ring benzocyclobutenone has been prepared by FVP from a simple benzoyl chloride precursor.