Interstellar silicon-nitrogen chemistry. I. The microwave and the infrared signatures of the HSiN, HNSi, HSiNH2, HNSiH2 and HSiNH+ species

Abstract

The experimental and the theoretical interests for the silicon chemistry have been renewed by the recent detection of SiN in space. In this contribution a theoretical study of the HSiN, HNSi, HSiNH 2 and HNSiH 2 molecular systems is presented that aims to help in the interpretation of available experimental results as well as in the attribution of new interstellar lines. The main goal of this report remains, however, the calibration of ab initio calculations on still-unknown silicon-nitrogen systems: the infrared and the microwave signatures of the HSiNH + cation are reported as a direct application. The signatures of the five molecules under investigation have been computed a t increasing levels of post-Hartree-Fock theories, using up to a 6-311 +-t-G * * atomic orbital expansion. Accurate geometries and B e rotational constants have been determined at the M~511er-Plesset MPn (n = 2, 3, 4), CASSCF and CCSD(T) theoretical plateaus for HNSi. The comparison with experimental data allows then to derive the scaling factors needed to obtain accurate rotational constants for related species: they are applied as such on the crude constants determined for HSiN, HSiNH 2, HNSiH 2, and finally HSiNH 2 in its floppy linear singlet ground state and in its lowest cis-bent a3p(state as well. Dipole moments are reported in order to assess the feasability for these species to be detected owing to their rotational signatures either in the laboratory or in space using millimetric radioastronomy techniques. Infrared (IR) signatures are computed at the same levels of theory and compared to the recent matrix isolation experiments devoted to HSiN, HNSi, HSiNH 2 and HNSiH 2. The calculations unambiguously confirm that all these species have been effectively produced and observed. They also lead to the determination of accurate IR scaling factors that are significantly larger than the usual ones. Such an approach allows then to quantitatively predict the IR spectra of the still-unknown HSiNH ÷ entity. The study of the IR spectra furthermore points out the failure of single-reference correlation methods to obtain predictive IR signatures in some cases, as is unambiguously illustrated in the case of the HSiN species.

H2NSi radical: structures, isomerization pathways and electronic states characterization

“…(ii) Silicon in astrophysical media either embedded in grains or in gas phase. This domain gained in interest since the detection of SiN in the outer circumstellar envelope IRC +10216 in 1992 by Turner [8] (iii) Silicon atoms and Si + ions in gas phase and porous glass surfaces reactivity against ammonia for the production of a wide variety of Si x N y H z molecules and for catalysis [9][10][11]. (iv) Such molecules in the formation of polysilane materials [12] with, for instance, non linear optics properties.…”

“…Parisel, Hanus and Ellinger [11,[13][14][15], they characterized three stable forms, namely HSiNH + , H 2 NSi + and H 2 SiN + , using multiconfigurational, Møller-Plesset MPn (n=2, 3,4) and Coupled Clusters approaches. They derived the IR and µw spectra of these cations in order to assign the available experimental data and for predictive purposes for astrophysical detections (See Refs.…”

“…They derived the IR and µw spectra of these cations in order to assign the available experimental data and for predictive purposes for astrophysical detections (See Refs. [11,13,15] for more details). In contrast, very few is known on the structure, the isomers, the energetics and the spectroscopy of the H 2 NSi neutral tetratomic molecule.…”

High-resolution rotational spectroscopy of iminosilylene, HNSi

“…Many electronic structure calculations [11][12][13][14][15][16][17][18] have been carried out on the HSiN-HNSi potential energy surface, the latest and most comprehensive being that of Lind et al [1]. In that study, relative energies, barrier heights to isomerisation, optimised geometries, dipole moments, vibrational frequencies which include anharmonic corrections, vibrational isotopic shifts, and dissociation energies were calculated for both isomers by a variety of highly correlated ab initio quantum chemical methods.…”

Theoretical study of the substituent effects on structure and dissociation of RNSi and RSiN (R = H, Li)

“…Apeloig and Albrecht [11] studied the relative stabilities and energy barriers separating silanitriles (RSiN) and silaisonitriles (RNSi) using HF, MP2, MP4 and CASSCF methods. Parisel et al [12,13] published a series of papers on HSiN, HNSi, HSiNH 2 , HNSiH 2 and HSiNH ? molecules containing silicon and nitrogen to study the silicon chemistry in interstellar medium.…”