Compaction and Destruction Cross-Sections for α-Glycine from Radiolysis Process via 1.0 keV Electron Beam as a Function of Temperature.

Abstract

Glycine is an amino acid that has already been detected in space. It is relevant to estimate its resistance under cosmic radiation. In this way, a sublimate of glycine in α-form on KBr substrate was exposed in the laboratory to a 1.0 keV electron beam. The radiolysis study was performed at 40 K, 80 K, and 300 K sample temperatures. These temperatures were chosen to cover characteristics of the outer space environment. The evolution of glycine compaction and degradation was monitored in real time by infrared spectroscopy (Fourier-transform infrared) by investigation in the spectral ranges of 3500-2100, 1650-1200, and 950-750 cm-1. The compaction cross-section increases as the glycine temperature decreases. The glycine film thickness layer of ∼160 nm was depleted completely after ∼15 min at 300 K under irradiation with ∼1.4 μA beam current on the target, whereas the glycine depletion at 40 K and 80 K occurred after about 4 h under similar conditions. The destruction cross-section at room temperature is found to be (13.8 ± 0.2) × 10-17 cm2, that is, about 20 times higher than the values for glycine depletion at lower temperatures (<80 K). Emerging and vanishing peak absorbance related to OCN- and CO bands was observed in 2230-2100 cm-1 during the radiolysis at 40 K and 80 K. The same new IR bands appear in the range of 1600-1500, 1480-1370, and 1350-1200 cm-1 after total glycine depletion for all temperature configurations. A strong N-H deformation band growing at 1510 cm-1 was observed only at 300 K. Finally, the destruction cross-section associated to tholin decay at room temperature is estimated to be (1.30 ± 0.05) × 10-17 cm2. In addition, a correlation between the formation cross-sections for daughter and granddaughter molecules at 300 K is also obtained from the experimental data.