Absolute molecular flux and angular distribution measurements to characterize DNA/RNA vapor jets

Vapor jets of DNA and RNA bases (adenine, cytosine, thymine, and uracil) from an oven with a capillary exit have been studied in the intermediate regime between molecular and viscous flow corresponding to Knudsen numbers in the range 0.1 < 10. The temperature control method ensured stationary flow. Assuming the Knudsen hypothesis, the pressure of sublimated molecules in the oven was determined as a function of temperature and the transmission probability of the capillary (Clausing factor). Thus it was possible to relate the oven temperature and pressure to the total flux through the capillary, determined by measuring the total mass of DNA/RNA base molecules condensed on a cold surface intersecting the jet. The angular distribution of molecules in the jet has been also studied experimentally using an optical interference method. The measured profiles are in good agreement with Troitskii's [Sov. Phys. JETP 7 (1962)353] analytical law for (cos theta)(3/2) angular dependence in the intermediate regime with error functions associated with the mean free path between intermolecular collisions. (C) 2010 Elsevier B.V. All rights reserved.