Efficient multiphoton dissociation of CF3I+ in the metastable X-tilde 2E1/2 excited state using cw infrared laser radiation

Abstract

Evidence for the multiphoton dissociation of an electronic metastable state of CF3I+ with CO2 laser radiation is presented. Only those ions possessing sufficient internal excitation before irradiation can be dissociated. Photodissociation results primarily from resonant absorption by the nu1 vibrational mode of CF3I+ in the higher of the two, spin–orbit levels of the ground electronic state Xbar^2 E1/2. Only the lowest energy decomposition channel is observed; this yields CF ⁺ ₃ and I. Spin–orbit and vibrational relaxation compete with photodissociation. At CF3I pressures below 2×10^−7 Torr, the collisional relaxation rate is proportional to CF3I pressure kc = (3.1±0.4)×10^−9 cm^3 molecule^−3 sec^−1 with a zero pressure rate of 11.3±1.3 sec^−1. The latter rate sets an upper limit on the spin–orbit relaxation rate. The photodissociation probability varies with laser frequency, exhibiting a broad, structureless peak near 960 cm^−1. The initial photodissociation rate is proportional to laser irradiance kD = 0.80±0.08 sec^−1/W cm^−2. The photoproducts and laser frequency dependence are the same using either cw or pulsed irradiation. Ions were exposed to irradiances up to 120 W cm^−2 cw and fluences up to 1.6 J cm^−2 pulsed. Ion cyclotron resonance (ICR) techniques were used to store and detect the ions.

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