Relative quantum yield of I (2P1/2) in the tunable laser UV photodissociation of i-C3F7I and n-C3F7I: effect of temperature and exciplex emission

Wavelength-specific relative quantum yields of I* from pulsed laser photodissociation of i-C3F7I and n-C3F7I in the range 265–336 nm are determined by measuring the time-resolved infrared emission (λ=1.315 μm) from the atomic I(2P1/2→2P3/2) transition. The quantum yields of I* from i-C3F7I and n-C3F7I are constant and appear to be unity from 265–298 nm but decrease to 0.57 and 0.40, respectively, at 336 nm. The lower quantum yields suggest the existence of two distinct bands in this region of the absorption continua. To determine the quantum yields a correction is made for enhanced emission due to formation of exciplexes between I* and the parent (i- or n-C3F7I) species. The exciplex emission increases linearly with parent gas pressure, but decreases with increasing temperature. For both molecules the integrated absorption in the long wavelength region (≳290 nm) increases substantially with temperature, while at selected wavelengths the quantum yields are found to remain constant with temperature. The results are discussed in terms of the development of solar-pumped iodine lasers.