A Spectroscopic and ab initio Study of the Hydrogen Peroxide–Formic Acid Complex

Abstract

The hydrogen-bonded complex between hydrogen peroxide and formic acid was studied by rotational spectroscopy and ab initio calculations. Because of the simplicity, chemical activity, and importance of hydrogen peroxide, it is a prototypical molecule to study intermolecular interactions, in particular hydrogen bonding. This work provides microscopic descriptions of the hydrogen peroxide–formic acid binary complex, which potentially could benefit much future work. Details of theories and experimental principles, including the setup of the cavity-based and chirped-pulse Fourier-transform spectrometers, are described. Also, a background of hydrogen peroxide and the reasons for studying its complex with formic acid are discussed. The results indicate that the most stable geometry of the hydrogen peroxide – formic acid binary complex includes a 7-membered ring-like hydrogen bonded structure, which is the only conformer found in the experimental work. In the spectrum of the complex a splitting of rotational transitions is observed, which is attributed to a tunneling motion of the non-hydrogen bonded hydrogen atom of hydrogen peroxide. Analyses of the electron density topology show that the complex is held together by two strong hydrogen bonds, where hydrogen peroxide slightly favors being a proton acceptor than a donor.