In the present article we have investigated the possibility of forming propylene oxide (PO) from propylene (PE) by bi-molecular reactions. Propylene oxide is the first chiral molecule observed in the interstellar medium, and studying the thermodynamics and kinetics of formation can suggest possible synthetic routes. We have focused our attention on gas phase reactions, and the presence of an environment is discussed in particular for the possibility of forming it by association reactions. In particular, we have considered radical and ion-molecule reactions. Results show that the main gas-phase route to PO formation is represented by ion-molecule reactions which turn out to be compatible with astrophysical conditions, notably: PE + O + and PE + HO + 2. Their final product is not PO, but its ionized variant PO + that can be neutralized by electron capture. The only thermodynamically and kinetically allowed reaction which can directly lead to neutral PO is a collision of PE with a singlet-excited OH + but two competing reactions (leading to PE + and PO +) are thermodynamically favored and thus more plausible in space.

Nitrogen is commonly implanted in silicon to suppress the diffusion of self-interstitials and the formation of voids through the creation of nitrogen–vacancy complexes and nitrogen–nitrogen pairs. Yet, identifying a specific N-related defect via spectroscopic means has proven to be non-trivial. Activation energies obtained from deep-level transient spectroscopy are often assigned to a subset of possible defects that include non-equivalent atomic structures, such as the substitutional nitrogen and the nitrogen–vacancy complex. Paramagnetic N-related defects were the object of several electron paramagnetic spectroscopy investigations which assigned the so-called SL5 signal to the presence of substitutional nitrogen (NSi). Nevertheless, its behaviour at finite temperatures has been imprecisely linked to the metastability of the NSi center. In this work, we build upon the robust identification of the SL5 signature and we establish a theoretical picture of the substitutional nitrogen. Through an understanding of its symmetry-breaking mechanism, we provide a model of its fundamental physical properties (e.g., its energy landscape) based on ab initio calculations. Moreover by including more refined density functional theory-based approaches, we calculate EPR parameters (↔g and ↔A tensors), elucidating the debate on the metastability of NSi. Finally, by computing thermodynamic charge transition levels within the GW method, we present reference values for the donor and acceptor levels of NSi.