# Why don't we use ionized neon for arc jets?

On a typical arc jet there is a cone in the proppelent stream (ammonia or hydrazine) that acts as an anode and the the nozel itself is the cathode. But why don't we use ionized neon as the cathode and still the cone as the anode, wouldn't that have a higher specific impulse and efficiency. Maybe even possibility of a ground launch. Also neon has the highest expansion ratio of any gas, I looked online everywhere and couldn't find any information about this.