Thermal reaction and luminescence of long-lived N <sup>2</sup>D in N<sub>2</sub> ice.
basic_science · Level V
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- Record sourced from PubMed, PMID 31732669.
- Also identified by DOI 10.1073/pnas.1910647116 and PMC identifier 6900521.
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Abstract
Photochemistry of an N<sub>2</sub> ice and thermal reaction of the irradiated sample were studied with vacuum-ultraviolet (VUV) light from a synchrotron. Concurrent detection of infrared absorption and visible emission spectra provide evidence for the generation of energetic products N (<sup>2</sup>D) and N (<sup>2</sup>P) atoms, N<sub>2</sub> (A) molecule and linear-N<sub>3</sub> (<i>l</i>-N<sub>3</sub>) radical after excitation of icy N<sub>2</sub> at 121.6 nm. Irradiation at 190 nm is shown to be an effective way to eliminate the <i>l</i>-N<sub>3</sub> radical. After the photolysis and photoelimination of the <i>l</i>-N<sub>3</sub>, we initiate synthesis of <i>l</i>-N<sub>3</sub> via the thermal ramping of the sample in temperature range 3.5 to 20 K. In addition, the emission from the N (<sup>2</sup>D) atom was observed during the thermal ramping process. These behaviors indicate that a long-lived N (<sup>2</sup>D<sub>long</sub>) atom is generated in the VUV-photolyzed N<sub>2</sub> ice. A comparison of the variations of the visible emission of N (<sup>2</sup>D) and the infrared absorption of <i>l</i>-N<sub>3</sub> with time indicates that the long-lived N (<sup>2</sup>D<sub>long</sub>) dominated the thermal synthesis of <i>l</i>-N<sub>3</sub> The results have enhanced suggestion and understanding of the conversion for nitrogen species in cold astrophysical environments with VUV irradiation.