EFFECTS OF BACKGROUND GASES ON THE HOMOGENEOUS NUCLEATION OF VAPORS .2.

Using a high-pressure, upward thermal diffusion cloud chamber, we have observed a strong dependence of the homogeneous nucleation of methano l, ethanol, and 2-propanol vapors on total pressure. In our investigat ion, this dependence is manifested by increasing values of the measure d S-crit (critical supersaturation) for each of the three alcohols wit h increasing total pressure (P-tot). The increase in total pressure is accomplished by increasing the amount of a background.(or carrier) ga s in the diffusion cloud chamber. The observed increase in measured S- crit implies that the homogeneous nucleation rate of each of these alc ohols decreases as the total pressure increases. We have observed a si gnificant dependence on the nature of the background gas. The effect o f increasing total pressure on the nucleation of each of these alcohol s is greater using helium as the background gas than when hydrogen is used. We also observe that the dependence of S-crit on total pressure (as manifested by the slope of the S-crit vs P-tot data at constant te mperature) is temperature dependent for each of these alcohols. The me asured slope of the S-crit vs P-tot dependence increases as the temper ature decreases.