Knowledge Bank

We have recorded the photoelectron spectrum of $P2-$ using a cold-cathode discharge ion source and a negative ion photoelectron spectrometer. We obtain a highly structured spectrum from which we have determined the electron affinity of $P2$ to be $0.589\pm 0.025eV$. Using this value for the electron affinity of $P2$ along with the electron affinity of P and the bond dissociation energy of $P2-$ in a thermochemical cycle, the bond dissociation energy of $P2$ is calculated to be $4.88\pm 0.06eV$. A Franck-Condon analysis of the spectrum was used to confirm peak assignments and to determine spectroscopic parameters for $P2-$. We find $we\prime \prime (P2-)=640\pm 50cm-1$ and $Be\prime \prime (P2-)=0.2776\pm 0.0028cm-1$ which leads to $Re\prime \prime (P2-)=1.979\pm 0.010A$. The positive electron affinity which we have measured for $P2$ compared to the non-positive electron affinity of $N2$ emphasizes the often noted electronic differences between phosphorus and nitrogen.