The full quote in wikipedia is

"the gas is first heated to a “cold plasma” by a helicon RF antenna/couple that bombards the gas with electromagnetic energy, at a frequency of 10 to 50 MHz, stripping electrons off the propellant atoms and producing a plasma of ions and free electrons."

bold mine.

The infrared radiation heats the gas, which means transfers kinetic energy to the atoms. The energy distribution of the atoms of the heated gas will have a high kinetic energy tail which allows through scatterings between atoms to ionize the atoms.

The full quote in wikipedia is

"the gas is first heated to a “cold plasma” by a helicon RF antenna/couple that bombards the gas with electromagnetic energy, at a frequency of 10 to 50 MHz, stripping electrons off the propellant atoms and producing a plasma of ions and free electrons."

bold mine.

The radiation heats the gas, which means transfers kinetic energy to the atoms. The energy distribution of the atoms of the heated gas will have a high kinetic energy tail which allows through scatterings between atoms to ionize the atoms.