S4N4was photolyzed by the KrF excimer laser source at 248 nm. The excited state photofragments produced are the NS(Bthinsp;2Pgr;)rand NS(Hthinsp;2Pgr;)1/2, NS(Gthinsp;2Sgr;minus;) and NS(Ithinsp;2Sgr;+) states. Single band progression fluorescence out ofvrsquo;=0 for NS(H)1/2andvrsquo;=2 for NS(G,I) are observed. Franckndash;Condon factors have been calculated for NS(H) up tovrsquo;=3. The electronic transition moment for the NS(Hndash;X) transition was found to decrease slightly with increasingrmacr;. The radiative lifetime of the 0,5 band of NS(H)1/2is determined to be 87plusmn;11 ns. The collisional quenching constants at 335 K for various species including N2(kq=3.4plusmn;0.7times;10minus;10cm3thinsp;sminus;1), CF4(kq=1.8plusmn;0.4times;10minus;10cm3thinsp;sminus;1), SF6(kq=3.9plusmn;0.7times;10minus;10cm3thinsp;sminus;1) and He (kq=5.6plusmn;2.2times;10minus;11cm3thinsp;sminus;1) are reported. A semiempirical calculation using a PM3 Hamiltonian was used to calculate the heats of formation of various (SN)xspecies. A mechanism is proposed to account for the presence of these excited states based on laser fluence, excited state time histories, spectral composition and calculated heats of formation. NS(B) is postulated to arise directly from an intermediate photolysis product which is assumed to be acyclic S3N3. The NS(Hthinsp;2Pgr;)1/2subband, NS(Gthinsp;2Sgr;minus;) and NS(Ithinsp;2Sgr;+) states are thought to be produced from a resonant interaction with the KrF line at 248 nm and vibrationally excited ground state NS. Using theI2(Drsquo;2gminus;A2u) emission as an actinometer, the overall efficiency on the conversion of absorbed photons by S4N4into NS(Bthinsp;2Pgr;) is 2.6plusmn;0.7percnt;.
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