Synthesis and infrared characterization of Br–HBr and Br–DBr entrance channel complexes in solid parahydrogen

Abstract

We report high resolution vibrational spectra in the HBr (2560 cm⁻¹) and DBr (1840 cm⁻¹) stretching regions for Br–HBr and Br–DBr entrance channel complexes isolated in solid parahydrogen (pH₂). The Br–HBr complexes are generated by synthesizing solid pH₂ crystals doped with trace amounts of HBr/Br₂ mixtures followed by 355 nm in situ photodissociation of Br₂ to form Br atoms. After photolysis is complete, the solid is warmed from 2 to 4.3 K resulting in the irreversible formation of Br–HBr complexes. The large 36.63 cm⁻¹HBr monomer-to-complex induced vibrational shift to lower energy measured in these studies is consistent with the linear Br–HBr hydrogen bonded structure predicted from theory. The 0.02 cm⁻¹Br–HBr absorption linewidths indicate a 1 ns vibrational excited state lifetime for these entrance channel complexes in solid pH₂.