  We have identified nitromethane (CH$_3$NO$_2$) as an effective electron
capture agent for negative ion TPCs (NITPCs).
  We present drift velocity and longitudinal diffusion measurements for
negative ion gas mixtures using nitromethane as the capture agent.
  Not only is nitromethane substantially more benign than the only other
identified capture agent, CS$_2$, but its low atomic number will enable the use
of the NITPC as a photoelectric X{}-ray polarimeter in the 1{}-10 keV band.
