Ultraviolet radiation from strong shocks

Abstract

Ultraviolet radiation studies at Avco-Everett Research Laboratory will be reviewed. They have been used in three ways: (1) chemical kinetic studies of high temperature air; (2) bremsstrahlung and molecular radiation in the windowless u.v. region from 300 Å—1200 Å; and (3) a fast bolometer to measure from 20 μ—20 Å gas radiation. The dissociation and vibration excitation rates of O2 and NO have been determined by measuring the transmission of u.v. radiation at 1470 Å and 1270 Å through shocks in air and component gases. In these studies it is necessary to understand the temperature dependence of the absorption coefficients, e.g., that of oxygen at 1470 decreases with increasing temperature. At 1270 Å there is a strong absorption by a high vibration state of nitrogen which is probably related to the b'1Σ → X1Σ transition with an electronic f-value of about 0·1. In the windowless u.v. region we have used a tungsten photoelectric absorption gauge and studies have been made of the radiation from shocks in air at 0·7 cm/μsec and in hydrogen at 25 cm/μsec. The measurements of the u.v. component from air shocks have been correlated with the absorption measurements at 1270 by vibrationally excited molecular nitrogen. The fast bolometer has a thin layer of carbon which is black from 20 μ to 20 Å. The radiation absorption is determined by observing the temperature rise of the absorber by observing the i.r. emission from its back. This gauge will work in the presence of strong electric and magnetic fields and has a rise time of less than 0·1 μsec.