Abstract
Shock layer radiation is observed in the wavelength range from vacuum-ultraviolet (VUV) to near-infrared (NIR) using a free-piston double-diaphragm shock tube. In the VUV region, atomic lines of N and C are predominant and no molecular band spectra are seen. In the ultraviolet (UV) region, the molecular bands of N2(2+) and N2+(1−) systems are predominant. In the visible (VIS) and NIR regions, atomic lines of N are intense, and weak molecular bands of the N2(1+) system are seen. The spectrum in the VUV region becomes more intense than that in the UV region with increasing shock velocity. On the other hand, the spectrum in the UV region is almost same with increasing shock velocity. The measured spectrum is analyzed using the radiation analysis code SPRADIAN 2. The analysis shows that the numerical spectrum can reproduce the measured one when the electronic excitation temperature is higher than the vibrational temperature. The electronic excitation temperature is evaluated from the atomic lines of nitrogen in a wide wavelength range and the spatial distribution is obtained. The result shows the electronic excitation temperature is higher than the vibrational temperature immediately behind a shock wave, consistent with the result obtained from the spectrum analysis.
