Radiative relaxation rate determination by competitive photodissociation of n-butylbenzene ions

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Abstract
The radiative relaxation rate of n-butylbenzene ions was measured using competitive photodissociation as a thermometric tool. Cooling curves showing the loss of internal energy of the ions with time were obtained at three pressures. An infrared radiative cooling rate of 0.5 s−1 was obtained from the data. This value is comparable to other cooling studies done in polyatomic ions having internal temperatures of the order of 200 K above room temperature. The radiative cooling of polyatomic molecules is compared with that of diatomics. Observations are in accord with theoretical expectations in showing that for polyatomics the infrared radiative cooling rate constants are slow and strongly dependent on internal temperature, in contrast to diatomics where they are fast and temperature independent.