The fluorescence excitation spectrum of the ArI2 van der Waals complex

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Abstract
The van der Waals molecule ArI2 has been produced in a supersonic expansion of I2 in mixed argon–helium carrier gas, and its fluorescence excitation spectrum has been observed. Spectra of the complex are only observed when the iodine stretching vibration is exicted to v′?12 in the excited ? electronic state. Above this value the intensity of the van der Waals spectrum is observed to be an oscillatory function of the iodine vibrational quantum number. This behavior is attributed to competition between two decay channels in the excited state: vibrational predissociation with a cross section that increases monotonically with v′, and electronic predissociation with a cross section that oscillates with v′. The spectral linewidth provides a lower limit of 3×10−11 sec for the lifetime of the excited state involved in the 0–15 transition.