Theoretical study on PCCCP and its isomers

The structures and isomerization pathways of singlet and triplet PC3P isomers are investigated at the DFT/B3LYP/6-311G(d) level. Among the 23 triplet and 18 singlet isomers, the global minimum is PCCCP 31 with ∑g−3 electronic state. It can be viewed as resonance structures among |PC-CC-P|, |PCCCP|, and |PC-C-CP|. Additionally, chainlike isomer 1PCPCC, ring isomers 1PC-cCCP, 1CC-cCPP, c1PCPCC, c1PCCCP, and cage-like isomers cage-1PPCCC and cage-1PCPCC also posses considerable kinetic stability. These eight isomers are predicted to be possible candidates for future experimental and astrophysical detection. Furthermore, the QCISD/6-311G(d) and DFT/B3LYP/cc-pVTZ calculations are performed on the structures and harmonic vibrational frequencies of the relevant species so as to aid their future laboratory and interstellar detection.