Journal Article

PUBDB-2025-05271

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Cryogenic Infrared Action Spectroscopy of [H$_2$NCO]$^+$ and [H$_2$NCS]$^+$ , Protonated Forms of Interstellar HNCO and HNCS

Gerlach, M. (Corresponding author) ; Schneider, N. R. ; Petrić, S. ; Kaur, H. ; Changala, P. B. ; Redlich, B.DESY* ; Brünken, S. (Corresponding author)

2025
American Chemical Society Washington, DC

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Please use a persistent id in citations: doi:10.1021/acs.jpca.5c04708  doi:10.3204/PUBDB-2025-05271

Abstract: HNCS, isothiocyanic acid, and HNCO, isocyanic acid, are important molecules in the interstellar medium due to their composition of the essential atoms for organic life and their possible prebiotic role. They are assumed to be formed by dissociative recombination of their protonated versions, [H$_2$NCO]$^+$ and [H$_2$NCS]$^+$, where protonation may occur either on the N- or the O/S-atom. Here, we report the investigation of [H$_2$NCO]$^+$ and [H$_2$NCS]$^+$ by broadband infrared (IR) spectroscopy in a cryogenic 22-pole ion trap instrument via tag-free leak-out spectroscopy. Infrared radiation in the range of 450–3500 cm–1 was provided by the infrared free-electron laser FELIX-2 at HFML–FELIX. We predominantly observe the N-protonated isomers, H$_2$NCS$^+$ and H$_2$NCO$^+$, with potentially a small contribution of H$_2$NCOH$^+$. Five fundamental transitions in the range of 450–3500 cm$^{–1}$ were observed of H$_2$NCO$^+$ and eight fundamental and overtone/combination bands of H$_2$NCS$^+$. The transitions are assigned with the help of quantum-chemical calculations using a combination of CCSD(T)/cc-pCVTZ for anharmonic transition energies and ωB97XD/cc-pVQZ for anharmonic transition intensities. Several modes show a rotational substructure, which is discussed in detail for the ν$_5$(b$_1$) bending vibrational mode of H$_2$NCS$^+$. The data presented in this paper is the first experimental study investigating the IR spectra of these ions and also the first experimental investigation of [H$_2$NCS]$^+$. This work provides important reference data for upcoming studies of formation mechanisms of HNCO and HNCS at cryogenic conditions.

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Contributing Institute(s):

1. Bereichsleitung FS (FS)

Research Program(s):

1. 631 - Matter – Dynamics, Mechanisms and Control (POF4-631) (POF4-631)

Experiment(s):

1. Measurement at external facility

Appears in the scientific report 2025

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