  We carry out plasma diagnostic analyses for 123 planetary nebulae (PNe) and
42 H II regions using the N II and O II optical recombination lines (ORLs). New
effective recombination coefficients for the N II and O II optical
recombination spectra are used. These data were calculated under the
intermediate coupling scheme for a number of electron temperature (Te) and
density (Ne) cases. We used a new method to determine the Te and Ne for the
nebular sample, combining the ORLs with the most reliable measurements for each
ion and the predicted intensities that are based on the new atomic data.
Uncertainties of the derived Te and Ne are estimated for each object. The
diagnostic results from heavy element ORLs show reasonable agreement with
previous calculations in the literature. We compare the electron temperatures
derived from the N II and O II ORLs, Te(ORLs), and those from the collisionally
excited lines (CELs), Te(CELs), as well as the hydrogen Balmer jump, Te(H I
BJ), especially for the PNe with large abundance discrepancies. Temperatures
from He I recombination lines, Te(He I), are also used for comparison if
available. For all the objects included in our sample, Te(ORLs) are lower than
Te(H I BJ), which are in turn systematically lower than Te(CELs). Nebulae with
Te(He I) available show the relation Te(ORLs) < Te(He I) < Te(H I BJ) <
Te(CELs), which is consistent with predictions from the bi-abundance nebular
model postulated by Liu et al. (2000).
