Structural Elucidation of N2O Clusters at Low Temperatures: A Matrix Isolation IR Spectroscopic and Computational study

Studies on the structures of nitrous oxide (N₂O) and its clusters on Earth and in space are of interest primarily due to their astrochemical and atmospheric relevance. Being isoelectronic with CO₂, N₂O has a huge impact on atmospheric chemistry as it is one of the greenhouse gases that is found in the terrestrial troposphere[1] and, in the case of exoplanets, scientists consider N₂O to be a potential remote biosignature for Earth-like planets, along with O₂, O₃, and CH₄ [2,3].

The present study investigates the interactions that bind N₂O molecules together within their aggregates at low temperatures using matrix-isolation infrared spectroscopy[4] coupled with insights from ab initio computations. The pnicogen character of the central nitrogen atom(s) is a major factor in determining the aggregation of N₂O molecules and is substantiated by molecular topography that contributes to the stability. N₂O is a very small molecule; it exists as a dimer even at room temperature favouring cluster formation at low temperature.

Spectral fingerprints in near-IR and mid-IR spectra are the key to the spectroscopic structural characterization of N₂O and its aggregates [5,6]. A number of previous studies have reported the formation of N₂O ices in various astrophysical environments[7], as it is considered to be an important tracer to quantify and characterize the abundance of N₂ in extraterrestrial environments [8].

Furthermore, astrophysical N₂O ice analogues have been bombarded by energetic electrons and ions to check the radiation stability of N₂O ice by Almeida et al.[9], and very recently by Mifsud et al.[10], and the resultant dissociation products (NO₂, NO and O₃) have been characterized by FT-IR spectroscopy. Recently, N₂ ice has been discovered by NASA in the atmosphere of Pluto[10], which can lead to the formation of N₂O ice by reacting with an excited O atom, as suggested by Jamieson et al.[11]. A number of groups have studied the structure of the N₂O molecule and its aggregation behaviour under matrix isolated conditions in solid N₂[12], Ar[13], Xe[14], Ne[15] p-H₂[16] matrices.

Previous studies have examined the structure of N₂O clusters but have not quantified the forces holding them together, generally attributing them to van der Waals or dipole-dipole interactions. This study explores the possibility of pnicogen bonding due to the unique electronic structure of N₂O. Dimers and trimers of N₂O were synthesized at low temperatures in an argon matrix and analyzed using infrared spectroscopy and ab initio methods. The findings offer new insights into the nature of the interactions stabilizing these clusters, which will be discussed further at the meeting.

 

Fig. 1: Matrix isolation IR spectra of N=N stretching region (left) and of N-O stretching region (right) of N₂O in Ar matrix using both effusive and supersonic molecular beam techniques. 

 

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