Vibrational deexcitation of molecular oxygen in a condensation flow

Abstract

In the present work the vibrational deexcitation time for the O z molecule has been studied in a more direct way: absorption spectroscopy. The experiment was conducted on a shock t.ube with a low-pressure chamber of 493 mm inside diameter and length 13 m. The chamber is made of stainless steel. The threemeter-long l~gh-pressure chamber has an inside diameter of 90 mm and is joined to the low-pressure section by a 30 ~ conical adapter. The driver gas is hydrogen (70~0) combined with a detonating mixture (30~o). At the time of an experiment the detonating mixture was ignited by a spark simultaneously at several points located along the axis of the high-pressure chamber. The low-pressure chamber was filled with oxygen which had first been cleaned by fractionation using liquid nitrogen cooling. Before filling, the low-pressure chamber was pumped to a pressure of about 1() -2 torr. Pumpdown with periodic freezing out of water vapor formed during the experiment was possible due to a leak and desorption rate from the chamber walls of tess than 10 -4 torr per minute. The speed of the incident shock wave was measured using three piezoelectric probes mounted in the wall of the tube directly in front of the nozzle location. The oscilloscopes used to record the shock speed and the absorption of ultraviolet radiation in the nozzle were triggered by the signal from a piezoelectric probe located 1 m from the test section. A reflecting wall with a plane 30 ~ nozzle (which has a critical cross section height of 2 ram) in its center was located in the test section of the shock tube. The convergent channel of the nozzle had a radius curvature of 4 ram. Oxygen, heated in the incident and reflected shocks, entered the nozzle. The absorption of UV at Z =2245 A was recorded at two cross sections of the nozzle: A/,%* =5.75 and 15, where A* is the critical cross section. The absorption coefficient of oxygen at h=2245 A is known [3, 4], and, al-. though the density of absorbing particles in the nozzle decreases rapidly, we have because of the ~arge optical path been able to obtain oscilloscope traces of the absorption even at relatively low temperatures and pressures in the reservoir (behind the reflected shock wave). The experiments were carried out for low initial conditions in the reservoir: p0 '= 7.4 aim, To'= 2260~ and p0 ''= 3.7 atm and To"= 2560~ These parameters of the reflected shock were calculated using the experimentally measured values of the incident shock speed, the conservation laws, and the equation of state. An example of the oscilloscope Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp.