Knowledge Bank

Energy transfer from specific rotational levels (quantum Number $N\prime$;) of $v\prime =1$ of the $A2\Sigma +$ state of the hydroxyl radical has been studied. The environment is the burnt gases ($\sim 70$) of a $Ch4/air$ flame at $T=1900$ K and atmospheric pressure. A tunable laser populates seven individual levels in the range $N\prime =1$ to 16, and rotationally resolved fluorescence measurement are made with a scanning monochromator. The energy transfer rate is found to decrease with increasing $N\prime$. The rotational population distribution for molecules transferred into $v\prime =0$ is thermal-like ($T\sim 2200 $K)foraninitialN‘=1,5and10inv‘=1butmuchhotter($T\sim3400 $K)foraninitialN‘=13-16.Theratiooftherateofrotationalenergytransferwithinv‘=1,tothequenchingrate,decreasesrapidlyovertherangeN‘=13to16,whichspansthepredissociationlimit.Adefinitepropensityfortransfertonearbylevels,andformaintaining,spincomponent($F_{1} vs F_{2}$), is exhibited during rotational relaxation of the levels of high N`.