Infrared spectra of free radicals and protonated species produced in para-hydrogen matrices

Abstract

The quantum solid para-hydrogen (p-H2) has emerged as a new host for matrix isolation experiments. Among several unique characteristics, the diminished cage effect enables the possibility of producing free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms or free radicals that are produced in situ from their precursors upon photo-irradiation. Many free radicals that are unlikely to be produced in noble-gas matrices can be produced readily in solid p-H2. In addition, protonated species can be produced upon electron bombardment of p-H2 containing a small proportion of the precursor during deposition. The application of this novel technique to generate protonated polycyclic aromatic hydrocarbons (PAH) and their neutral counterparts demonstrates its superiority over other methods. The technique of using p-H2 as a matrix host has opened up many possibilities for the preparation of free radicals and unstable species and their spectral characterization. Many new areas of applications and fundamental understanding concerning the p-H2 matrix await further exploration.

The Infrared Spectrum of Protonated Ovalene in Solid Para-Hydrogen and Its Possible Contribution to Interstellar Unidentified Infrared Emission

“…The matrix-isolation system for mid-IR absorption and the p-H 2 converter used in this work have been described elsewhere (Lee et al 2006;Bahou et al 2012Bahou et al , 2014a. A gold-plated flat copper substrate, cooled to 3.2 K with a closedcycle helium refrigerator system (SHI, RDK-415D), served as both the matrix sample substrate and the mirror to reflect the incident mid-IR beam to the detector.…”

“…Recently, we have developed a new method to investigate the mid-IR spectra of H + PAHs and HPAHs using electron bombardment during deposition of PAH diluted in parahydrogen (p-H 2 ) at 3.2 K (Bahou et al 2014a). The bombardment of p-H 2 with electrons produces H 3 + and H, which subsequently react with PAH to form H + PAH and HPAH which are trapped in the p-H 2 matrix.…”

On the correlation of the abundances of HNCO and NH2CHO: Advantages of solid para-H2 to study astrochemical H-atom addition and abstraction reactions

“…H atoms can be conveniently generated in solid para-H 2 by simple photolytic methods (Raston & Anderson (2006); Bahou et al (2014)), e.g., by UV photolysis of Cl 2 , premixed with para-H 2 before deposition, followed by IR irradiation. Since the solid para-H 2 is a soft quantum matrix, due to the excess energy of the photons, the two Cl atoms can be separated and occupy two separate sites.…”

CN radical hydrogenation from solid H2 reactions, an alternative way of HCN formation in the interstellar medium

“…The reaction product was HCD 3 which demonstrates that H 2 can react with a radical forming the hydrogenated compound. Bahou et al (2014) studied the reaction of photoinduced radicals in a H 2 matrix.…”