Title: Resonant Electron Impact Excitation of 3d levels in Fe$^{14+}$ and Fe$^{15+}$,
Abstract: We present laboratory spectra of the $3p$--$3d$ transitions in Fe$^{14+}$ and
Fe$^{15+}$ excited with a mono-energetic electron beam. In the energy dependent
spectra obtained by sweeping the electron energy, resonant excitation is
confirmed as an intensity enhancement at specific electron energies. The
experimental results are compared with theoretical cross sections calculated
based on fully relativistic wave functions and the distorted-wave
approximation. Comparisons between the experimental and theoretical results
show good agreement for the resonance strength. A significant discrepancy is,
however, found for the non-resonant cross section in Fe$^{14+}$. %, which can
be considered as a fundamental cause of the line intensity ratio problem that
has often been found in both observatory and laboratory measurements. This
discrepancy is considered to be the fundamental cause of the previously
reported inconsistency of the model with the observed intensity ratio between
the $^3\!P_2$ -- $^3\!D_3$ and $^1\!P_1$ -- $^1\!D_2$ transitions.