Methoxyphosphinidene oxide (CH3 OPO) and isomeric methyldioxophosphorane (CH3 PO2 ) are key intermediates in the degradation of organophosphorus compounds (OPCs). Unlike the nitrogen analogues CH3 ONO and CH3 NO2 , the experimental data for these two prototypical OPCs are scarce. By high-vacuum flash pyrolysis (HVFP) of the diazide CH3 OP(O)(N3 )2 at 1000 K, the cis and trans conformers of CH3 OPO have been generated in the gas phase and subsequently isolated in cryogenic Ar and N2 matrices for IR spectroscopic characterization. Upon 266 nm laser irradiation of CH3 OPO, cis→trans conformational conversion occurs with concurrent isomerization to CH3 PO2 . The spectroscopic identification of CH3 OPO and CH3 PO2 is supported by D-, 13 C-, and 18 O-isotope labeling and quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction (VCI).
Keywords: IR spectroscopy; matrix isolation; organophosphorus compounds; phosphorus; photoisomerization.
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