Halides, Hydrogen Cyanide, and Cyanogen

Cyanogen Halides, Hydrogen Cyanide, and Cyanogen.—Studies of energy disposal in the near u.v. photodissociation of ICN have had a chequered career. In an early flash photolysis experiment it was concluded that CN was formed in its ground electronic state with little or no vibrational excitation. Subsequent theoretical treatments all agreed that this was a respectable conclusion but new 

CN(Jr S+) . o + lifP was discounted since more recent flash photolysis studies had not indicated any significant population of excited iodine atoms. 

Studies of vibrational (and rotational) energy disposal in the vacuum u.v. photodissociation of cyanogen, hydrogen cyanide, and the cyanogen halides, were reported by Mele and Okabe and the estimated vibrational distributions in the dissociations 

The vacuum u.v. photodissodation of BrCN has been studied using the technique of polarized photofluorescence exdtation spectroscopy. Measurements of the fluorescence polarization estaUished that the primary excited states leading to 

CN(B) were bent with A symmetry and with the transition dipole lying close to the C-Br axis. Hie measurements also indicated a shorter lifetime in vibronic states where the stretching motion was predominantly in the C—Br rather than the C—N bond and the predissociation lifetimes were estimated to be x 6 10 s. 

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