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).

Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen I: Anomalous Effect of Temperature

“…We presented IR spectra of all three modes of HCO in previous studies of the 193 nm in situ photolysis of N-methylformamide in solid pH 2 . 47 We show in Figure S2 in the SI detailed lineshapes of the ν 2 (CO stretch) and ν 1 (CH stretch) fundamentals of HCO at 1.65 and 4.36 K, which show better resolved spectra than previously reported. 47 We suspect the fine structure observed in both bands is due to hindered rotation and/or spin-rotation interactions.…”

“…47 We show in Figure S2 in the SI detailed lineshapes of the ν 2 (CO stretch) and ν 1 (CH stretch) fundamentals of HCO at 1.65 and 4.36 K, which show better resolved spectra than previously reported. 47 We suspect the fine structure observed in both bands is due to hindered rotation and/or spin-rotation interactions. This is the first report of HOCO in solid pH 2 , and accordingly we present all the observed spectral features in Table S2 and Figure S3; representative HOCO ν 1 and ν 2 IR spectra at low and high temperature are provided in Figure S4 (see SI).…”

The ALMA-PILS survey: detection of CH3NCO towards the low-mass protostar IRAS 16293−2422 and laboratory constraints on its formation

“…Henderson & Gudipati (2015) tentatively assigned a mass fragmentation peak to CH 3 NCO after VUV irradiating solid-state mixtures of NH 3 :CH 3 OH. In other experiments by Ruzi & Anderson (2012) UV irradiation of frozen n-methylformamide (CH 3 NHCHO) also yielded methyl isocyanate, although it was concluded to represent a minor product channel.…”

Infrared Spectroscopy and 193 nm Photochemistry of Methylamine Isolated in Solid Parahydrogen

“…12 By comparing the as-deposited spectra recorded in this work for a sample that contains only MA with the spectrum recorded after the partial photolysis of NMF in solid pH 2 , we can very quickly identify which peaks are due to MA. Comparison of the two different sets of data shows that whereas the earlier spectral data are for lower MA concentrations and complicated by infrared absorptions due to other photoproducts and by the NMF precursor, it is clear the assignment is correct and MA is one of the primary photoproducts of the 193 nm in situ photolysis of NMF.…”

“…First, we find that IR peaks assigned to MA in a previous 193 nm in situ photolysis study of NMF in solid pH 2 were correct except for one peak in the C− H stretching region that was misassigned. 12 Second, we show from nuclear spin-state resolved IR spectra of CH 4 and NH 3 that these species arise from the CH 3 and NH 2 photoproducts of channel 1c. In both cases we were able to detect the CH 3 and NH 2 intermediates to validate the proposed mechanism by which CH 4 and NH 3 are produced in the 193 nm in situ photolysis of MA.…”