Study Of NH And CH Supersonic Molecular Beams

Simple diatomic polar radicals, NH and CH, extensively exist in stellar atmospheres, interstellar space, plasma, (bio-) chemical reactions and flames, and thus play significant roles in the relative fields, such as astrophysics, plasma physics, environmental science, combust science and chemistry. Spectroscopy is an important method to gain the configuration parameters, energy levels and interaction information of free radicals. However, due to lower densities in the laboratory and shorter lifetime of the free radicals, they are difficult to be studied.In this paper, the NH radical molecular beam was generated by DC pulsed discharging the ammonia seeded in argon/helium in the supersonic expansion. Its emission spectra of (0, 0) and (1,1) bands in the system A³II-X³âˆ‘ and (0, 0) band in c¹II-a¹â–³ were measured with a set of stainless steel disc electrodes and two sets of tungsten and iron pinpoint electrodes, respectively. To optimize the experimental condition, the dependence of the spectral intensity of (0, 0) band in A³II-X³âˆ‘ on experimental parameters was studied. Additionally, the generation mechanism of NH radical was discussed, and the population ratio of vibrational 1st excited to ground in A³II was estimated to be N₁/N₀ = 0.3.The CH radical molecular beam was also generated by DC pulsed discharging the methane seeded in helium in the supersonic expansion in order to study the generation and features of CH. The dependence of the spectral intensity of CH on the ratio of methane in the mixture was studied at a total pressure fixed at 3 atm and a discharge voltage fixed at —4 kV. A theoretical model was proposed to interpret the experimental results. Thus, an optimal ratio of CH4 was determined to be about 1%. The delay time of discharge relative to the valve opening was determined to be about 460μs when the spectral intensity of CH was most intense. Moreover, by analyzing the intensity distribution of CH emission spectra of the (0, 0) band in the A² △—X²II system, the vibrational and rotational temperatures of CH (A²â–³) were determined to be about 4575K and 2455K, respectively, and the CH number was estimated to be about 10¹³¹0¹⁴ per pulse in our experimental condition.