Title: Infrared predissociation spectroscopy of cold trapped C2H-(H2) and C2H-(D2)
Authors: S. Purushu Melath, K. Dulitz, M. Hauck, D. Swaraj, F. Dahlmann, M. Gerlach, D. F. Dinu, P. Jusko, K. R. Liedl, S. Schlemmer, S. Brünken, R. Wester
DOI: 10.1080/00268976.2025.2564248
Date: 2025-10-07
Working Group: Working Group 5 Confined Systems in Astrochemistry
Grant Period: 3
Grant Period Goal (number): 8: [GAPG-8] analysis of astrochemical environments by the vibrational features in the infrared (IR) range, from isolated molecules to molecular complexes
Covered deliverables from the MoU (number): 14: Working Group 5. Spectroscopic characterization of astrochemical molecules
Countries involved: Austria, Sweden, the Netherlands, Germany
Number of female/young/ITC coauthors: female: 4, young: 8, ITC: 0
Is the publication open access?: Yes
Is the publication co-lead by a YRI?: No
Abstract: The vibrational spectra of cryogenically cooled acetylide anions, C2H-, tagged with H2 and D2 , are obtained over a wide spectral range spanning 350–3500 cm-1 . Using the FELIX infrared free electron laser in combination with the 22-pole ion trap instrument FELion, infrared predissociation (IRPD) spectroscopy of C2H-(H2 ) and C2H-(D2 ) complexes have been performed and compared to high-level ab initio calculations. The IRPD spectrum of the H2-tagged complex exhibits two transitions at 511(2) cm-1 and 1790(3) cm-1 , which are assigned to the fundamental C ≡ C-H bending and C ≡ C stretching modes of C2H-, respectively; a third spectral feature at 1014(2) cm-1 is ascribed to the first overtone of the C≡C-H bending mode of C2H-. Theoretical vibrational configuration interaction calculations for C2H- have been carried out on a four-mode potential energy surface at the CCSD(T)-F12/CVQZ-F12 level of theory. These results, as well as previously published computational results, validate the assignments. The influence of the H 2 /D2 messenger molecules on the band positions is found to be small. However, for C2H-(H2 ), additional spectral features are observed in the 700-900 cm-1 range, which are interpreted as overtone and/or combination bands of intermolecular vibrational modes between the H2 messenger molecule and the C2H- anion. Finally, a transition at 2860(3) cm-1 is assigned to the fundamental D-D stretching vibration inside the C2H-(D2) complex.
