NEGATIVE ION PHOTOELECTRON SPECTROSCOPY OF $P^{-}_{2}$

Address of Investigators: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218.Author Institution:We have recorded the photoelectron spectrum of $P^{-}_{2}$ 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 $P_{2}$ to be $0.589 \pm 0.025 eV$. Using this value for the electron affinity of $P_{2}$ along with the electron affinity of P and the bond dissociation energy of $P^{-}_{2}$ in a thermochemical cycle, the bond dissociation energy of $P_{2}$ is calculated to be $4.88 \pm 0.06 eV$. A Franck-Condon analysis of the spectrum was used to confirm peak assignments and to determine spectroscopic parameters for $P^{-}_{2}$. We find $w^{\prime\prime}_{e} (P^{-}_{2})= 640 \pm 50 cm-^{1}$ and $B^{\prime\prime}_{e}(P^{-}_{2}) = 0.2776 \pm 0.0028 cm-^{1}$ which leads to $R^{\prime\prime}_{e}(P^{-}_{2}) = 1.979 \pm 0.010 A$. The positive electron affinity which we have measured for $P_{2}$ compared to the non-positive electron affinity of $N_{2}$ emphasizes the often noted electronic differences between phosphorus and nitrogen