Improved positron-molecule binding energies and estimations using molecular parameters

Positron-molecule binding energies ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ have been measured for over 100 molecules. They range from a few to greater than 300 meV. The complete set of ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ values is presented including, where necessary, updated analyses of previous data to provide more accurate values of ${\ensuremath{\varepsilon}}_{\mathrm{B}}$. The result is a dataset of 85 distinct hydrocarbon molecules and 29 deuterated analogs with ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ values ranging in precision from $\ifmmode\pm\else\textpm\fi{}3$ to $\ifmmode\pm\else\textpm\fi{}20$ meV. Linear regression analysis is used to estimate ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ using the global molecular parameters polarizability $\ensuremath{\alpha}$, permanent dipole moment $\ensuremath{\mu}$, and the number of $\ensuremath{\pi}$ bonds ${N}_{\ensuremath{\pi}}$ associated aromatic molecules and those with unsaturated bonds. Use of an optimized expansion for the entire dataset predicts ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ to within a root-mean-square error of $\ensuremath{\approx}30$ meV. This expression can provide useful estimates of ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ for molecular species similar to those in the existing dataset but for which ${\ensuremath{\varepsilon}}_{\mathrm{B}}$ has not been measured. Chemical species for which this regression analysis is not valid are discussed. Complementary analyses are made for restricted ranges of global parameters, and these empirical expressions provide additional insight into the underlying physical mechanisms for positron-molecule binding. The results are related to recent many-body theory calculations of the bound-state positron wave functions.