Formic acid in deuterium and hydrogen matrices

ABSTRACT

Formic acid (HCOOH, FA) was studied experimentally, by infrared spectroscopy, in H₂ and D₂ matrices, with focus on the preparation and characterisation in these matrix media of structures containing the higher-energy (cis) conformer. The cis-FA monomer and the cis-FA^…N₂ complex were successfully produced by selective vibrational excitation of corresponding trans-FA based species, and vibrationally characterised. The tunneling-induced conversion of the cis-FA^…N₂ complex in the studied matrices into the corresponding trans-FA complex was also investigated, and the found tunnelling properties discussed, in particular in comparison with those observed for the spontaneous conversion of cis-FA monomer into trans-FA. This article constitutes the first report on the infrared spectrum of FA conformers and stability of cis-FA monomer in a D₂ matrix, and on the structure, spectroscopy and stability of the cis-FA^…N₂ complex in both H₂ and D₂ matrices. Different attempts to prepare the cis-FA^…H₂O complex in the two investigated matrices are also described in detail, both from previously in situ generated cis-FA monomer followed by thermal mobilisation and by direct selective vibrational excitation of the trans-FA-H₂O complex.

GRAPHICAL ABSTRACT

KEYWORDS:

• Formic acid
• conformational change
• matrix isolation
• infrared-induced conformational isomerisation
• hydrogen atom tunnelling

Acknowledgements

The authors acknowledge the financial support from the Portuguese ‘Fundação para a Ciência e a Tecnologia; (FCT) (Post-doctoral Grant ref. SFRH/BPD/77276/2011 and Project PTDC/QEQ-QFI/3284/2014 – POCI-01-0145-FEDER-016617) and from the Academy of Finland through the Project KUMURA (No. 1277993). The Coimbra Chemistry Centre (CQC) is also supported by FCT (Project UI0313/QUI/2013) and COMPETE-UE. We also thank the CSC–IT Center for Scientific Computing Ltd. (Espoo, Finland) for allocation of computer time.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors acknowledge the financial support from the Portuguese Fundação para a Ciência e a Tecnologia (FCT) (Post-doctoral Grant ref. SFRH/BPD/77276/2011 and Project PTDC/QEQ-QFI/3284/2014 – POCI-01-0145-FEDER-016617) and from the Academy of Finland through the Project KUMURA (No. 1277993). The Coimbra Chemistry Centre (CQC) is also supported by FCT (Project UI0313/QUI/2013) and COMPETE-UE.