Sensitivity of our modeled fluorescence efficiencies for some representative Ni I lines (top) and Fe I lines (middle) to heliocentric velocity, and (bottom) example velocity-sensitive line ratios for Ni I (black) and Fe I (red). Efficiencies were calculated for a heliocentric distance of 1 au. The heliocentric velocity of Hyakutake (−36.7 km s⁻¹) is shown as a vertical dashed line.