Generation and characterization of ionic and neutral P(OH) 2+/· in the gas phase by tandem mass spectrometry and computational chemistry

Abstract

The bicoordinated dihydroxyphosphenium ion P(OH) 2 + ( 1 +) was generated specifically by charge-exchange dissociative ionization of triethylphosphite and its connectivity was confirmed by collision induced dissociation and neutralization-reionization mass spectra. The major dissociation of 1 + forming PO + ions at m/ z 47 involved another isomer, OPOH 2 + ( 2 +), for which the optimized geometry showed a long POH 2 bond. Dissociative 70-eV electron ionization of diethyl phosphite produced mostly 1 + together with a less stable isomer, HP(O)OH + ( 3 +). Ion 2 + is possibly co-formed with 1 + upon dissociative 70-eV electron ionization of methylphosphonic acid. Neutralization-reionization of 1 + confirmed that P(OH) 2 · ( 1) was a stable species. Dissociations of neutral 1, as identified by variable-time measurements, involved rate-determining isomerization to 2 followed by fast loss of water. A competitive loss of H occurs from long-lived excited states of 1 produced by vertical electron transfer. The A and B states undergo rate-determining internal conversion to vibrationally highly excited ground state that loses an H atom via two competing mechanisms. The first of these is the direct cleavage of one of the OH bonds in 1. The other is an isomerization to 3 followed by cleavage of the PH bond to form OPOH as a stable product. The relative, dissociation, and transition state energies for the ions and neutrals were studied by ab initio and density functional theory calculations up to the QCISD(T)/6–311+G(3df,2p) and CCSD(T)/aug-cc-pVTZ levels of theory. RRKM calculations were performed to investigate unimolecular dissociation kinetics of 1. Excited state geometries and energies were investigated by a combination of configuration interaction singles and time-dependent density functional theory calculations.