BARC/PUB/10//0710

 
 

Dynamics of N-OH bond dissociation in cyclopentanone and cyclohexanone oxime at 193 nm: Laser-induced fluorescence detection of nascent OH (u”, J”)

 
     
 
Author(s)

Kawade, M. N.; Saha, A.; Upadhyaya, H. P.; Kumar, A.; Naik, P. D.

ABSTRACT

Cyclohexanone oxime (CHO) and cyclopentanone oxime (CPO) in the vapor phase undergo N-OH bond scission upon excitation at 193 nm to produce OH, which was detected state selectively employing laser-induced fluorescence. The measured energy distribution between fragments for both oximes suggests that in CHO the OH produced is mostly vibrationally cold, with moderate rotational excitation, whereas in CPO the OH fragment is also formed in u" =  0.J"). The rotational population of OH (u"= 0, J") from CHO is characterized by a rotational temperature of 1440 ± 80 K, whereas the rotational populations of OH (u" = 0, J") and OH (u" = 1, J") from CPO are characterized by temperatures of 1360 ± 90 K and 930 ± 170 K, respectively. A high fraction of the available energy is partitioned to the relative translation of the fragments with ¦T  values of 0.25 and 0.22 for CHO and CPO, respectively. In the case of CHO, the A-doublet states of the nascent OH radical are populated almost equally in lower rotational quantum levels N", with a preference for P+ (A') states for higher N". However, there is no preference for either of the two spin orbit states P3/2 and P1/2 of OH. The nascent OH product in CPO is equally distributed in both L-doublet states of P+ (A") and P- (A") for all N", but has a preference for the P3/2 spin orbit state. Experimental work in combination with theoretical calculations suggests that both CHO and CPO molecules at 193 nm are excited to the S2 state, which undergoes nonradiative relaxation to the T2 state. Subsequently, molecules undergo the N-OH bond dissociation from the T2 state with an exit barrier to produce OH (u", J").

 
 
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