Variations in the Sign of the Pressure-Induced Lineshifts in the v2 Band of Ammonia with Temperature

The self-collisional shift of the aP(6,O) and aP(6,1) lines of the infrared v2 ammonia band was measured as a function of temperature in the range 200-400 K. In agreement with theoretical predictions, the shift goes from negative (red shift) to positive (blue shift) with increasing temperature. Such a result must be taken into account in modelling the temperature dependence of pressure shift.