Infrared spectrum of CH₃⁺ involving high rovibrationai levels

An extensive search of carbo-ion spectra in the infrared region from 3300 cm −1 to 2900 cm −1 has revealed many spectral lines of CH 3 + , the most fundamental hydrocarbon cation. Out of over 1000 spectral lines that were identified as due to CH 3 + from their plasma chemical behaviors and linewidths, 356 lines have been assigned to the CH stretch ν 3 fundamental band. Most of the remaining lines are thought to belong to the hot bands ν 2 + ν 3 − ν 2 and ν 3 + ν 4 − ν 4 . Their analysis was found to be difficult because of the large Coriolis interaction and the near degeneracy of ν 2 and ν 4 . A series of spectral lines has been assigned to the ν 3 + ν 4 − ν 4 band. The rovibrational temperature of CH 3 + in the plasma has been determined from relative intensities of the spectral lines.