Efficient multiphoton dissociation of CF3I+in the metastableXtilde;thinsp;2E1/2excited state using cw infrared laser radiation

摘要

Evidence for the multiphoton dissociation of an electronic metastable state of CF3I+with CO2laser radiation is presented. Only those ions possessing sufficient internal excitation before irradiation can be dissociated. Photodissociation results primarily from resonant absorption by the ngr;1vibrational mode of CF3I+in the higher of the two, spinndash;orbit levels of the ground electronic state quest;thinsp;2E1/2. Only the lowest energy decomposition channel is observed; this yields CF+3and I. Spinndash;orbit and vibrational relaxation compete with photodissociation. At CF3I pressures below 2times;10minus;7Torr, the collisional relaxation rate is proportional to CF3I pressurekc= (3.1plusmn;0.4)times;10minus;9cm3moleculeminus;3secminus;1with a zero pressure rate of 11.3plusmn;1.3 secminus;1. The latter rate sets an upper limit on the spinndash;orbit relaxation rate. The photodissociation probability varies with laser frequency, exhibiting a broad, structureless peak near 960 cmminus;1. The initial photodissociation rate is proportional to laser irradiancekD= 0.80plusmn;0.08 secminus;1/Wthinsp;cmminus;2. The photoproducts and laser frequency dependence are the same using either cw or pulsed irradiation. Ions were exposed to irradiances up to 120 Wthinsp;cmminus;2cw and fluences up to 1.6 Jthinsp;cmminus;2pulsed. Ion cyclotron resonance (ICR) techniques were used to store and detect the ions.