Photodissociation of N-methylformamide isolated in solid parahydrogen

Abstract

We report FTIR studies of the 193 nm photodecomposition of N-methylformamide (NMF) isolated in solid parahydrogen (pH(2)) matrices at 1.9 K. By studying the detailed photokinetics we can distinguish between primary and secondary photoproducts. We observe single exponential decay of the NMF precursor upon irradiation and identify three competing primary dissociation channels: HCO + NHCH(3); H + CONHCH(3); and CO + CH(3)NH(2) with branching ratios of 0.46(7):0.032(8):0.51(6), respectively. Two of the primary photoproducts (NHCH(3) and CONHCH(3)) are observed for the first time using IR spectroscopy and assigned via ab initio calculations of the vibrational frequencies and intensities of these radicals. The dominant radical formation channel HCO + NHCH(3) is consistent with efficient C-N peptide bond fission at this wavelength and escape of the nascent radical pair from the pH(2) solvent cage. The significant branching 0.51(6) measured for the molecular channel CO + CH(3)NH(2) is unexpected and raises important questions about the details of the in situ photochemistry. Starting from the NMF precursor, we observe and characterize spectroscopically a wide variety of secondary photoproducts including CH(2)NH, HCN, HNC, HNCO, CH(3)NCO, CH(4), and NH(3).