Energy transfer from chloroimidogen (a1.DELTA.) to iodine atoms

Abstract

Mixtures of CH212 and ClN3 are photolyzed a t 193 nm to produce iodine atoms and NCl(alA), respectively. The collisional excitation of the iodine atoms to the 52Pl/2 state is readily observed from the time profile of chemiluminescence from this species. From a steady-state treatment of the intensities, the rate constant for the specific energy-transfer process (i.e., the excitation of the 12P1/2 state) is determined to be k = (1.8 f 0.3) X lo-" cm3 s-I. The branching fraction for production of 12Pl/2 in the overall quenching of NCl(alA) by iodine atoms has a lower limit of 0.25. Excited I2P1/2 is quenched by ClN3 with a rate constant kQ = (2.0 f 0.3) X lo-" cm3 s-I. From these rate constants and comparison of the I2P1/2 and NCl(a'A) time profiles, it is inferred that energy transfer from 12P1,2 to ClN3 regenerates both IzP3/2 and NCl(alA), such that cycling of the iodine atoms between the 2P1/2 and 2P3/2 states serves to drain the energy stored in the azide.

Advanced COIL--physics, chemistry and uses

“…In fact, both branching fractions for NCl(a 1 ¢) and I*( 2 P 1=2 ) production in reactions (12) and (13) are reported to exceed 50% [21,22]. In 1998, Herbelin and co-workers [23] reported a direct measurement of small signal gain on the I ( 2 P 3=2 )±I* ( 2 P 1=2 ) transition generated by energy transfer from NCl(a 1 ¢).…”

“…The energy transfer reaction between NCl (a 1 ¢) and ground state iodine atoms produces I*( 2 P 1=2 ) which is the source of the laser radiation [22]:…”

Photodissociation of Gaseous NCl3 at 193 and 249 nm

“…The excited iodine produced by direct photolysis of CH 2 I 2 has a detector limited rise followed by a slow exponential decay over several ms. The excited iodine produced by collisional excitation appears as an emission signal rising over a few hundred µs to a ms after the laser pulse (depending on the densities of the collision partners), followed once again by a slow decay over a few ms. Because the rate constant for excitation of iodine atoms to the 5 2 P 1/2 state by collisions with NCl(a 1 ∆) is known, 7,8 and the enhancement in the absolute number density of I(5 2 P 1/2 ) caused by such collisional excitation can be experimentally determined from the I(5 2 P 1/2 ) emission time profile (by using the time profile of excited iodine emission from phototdissociation of CH 2 I 2 as a standard), observation of the production of excited iodine atoms by 193 nm photolysis of mixtures of CH 2 I 2 and NCl 3 offers a means of determining the density of NCl(a 1 ∆) present, and hence the quantum yield for its production by photodissociation of NCl 3 . Figures 5A, B, and C show time profiles of 1315 nm iodine emission produced by the 193 nm photodissociation of CH 2 I 2 (diluted in Ar) and mixtures of CH 2 I 2 and NCl 3 (also diluted in Ar) under three different experimental conditions.…”

AsCl radical: The low-lying electronic states and the (1)3Π →X 3Σ− electronic transition

“…The AsCl radical is isovalent to diatomic haliminos, like, NCl [1], PF [2], PCl [3], AsF [4], and AsI [5] which have been studied as potential candidates for chemical energy storage systems, e.g. chemical lasers [1][2][3][4][5][6][7], since their metastable a 1 and b 1 + states could be produced in high concentration [1][2][3][4][5][6][7]. Therefore, the accurate characterization of the ground state (X 3 − ), as well as the a 1 , b 1 + states, among others should be important.…”