amongst the lowest characteristic temperatures and highest
oscillator strengths.
Chapter 2 : Ionisation processes and gas emissivities 65
H ow ever, th e r e e x is t a se rie s of s tro n g tr a n s itio n s , t h a t a re h ig h ly p o p u la te d a t th e e x p e rim e n ta l c o n d itio n s of in te r e s t, in th e n e a r in fra re d a ro u n d 777.0 nm .
F ig u re s 2.2, 2.3 a n d 2.4 show th e im p o rta n t p o te n tia l w ells resp o n sib le for th e d o m in a n t r a d ia tio n e m itte d by shock h e a te d a ir. F ig u re 2.2 sh o w s th e m o le c u la r d ia g r a m for N 2 a n d N 2+. T h e a rro w s a re in d ic a tiv e of th e s tro n g e s t e m ittin g b a n d s w h ich a re , in d e sce n d in g o rd er, th e firs t n e g a tiv e b a n d of N 2+ a n d th e firs t a n d second positive b a n d s of N 2. F ig u re 2.3 p r e s e n ts th e m o le c u la r d ia g ra m fo r th e S c h u m a n n -R u n g e tr a n s itio n of 0 2 a n d fig u re 2.4 show s th e p o te n tia l e n e rg y d ia g r a m fo r th e NO m o le cu le , h ig h lig h tin g th e ß a n d y
tr a n s itio n s . T o g e th e r w ith th e s e p o te n tia l cu rv e s v a rio u s re p u ls iv e p o te n tia ls a re d raw n . T h ese p o te n tia ls can act to d ecrease (d rain ) th e a m o u n t of em issio n v ia th e p re d isso c ia tio n of m olecules from a given s ta te . T he S c h u m an n -R u n g e tra n s itio n is especially v u ln e ra b le to th is process as th e re p u ls iv e 3n p o te n tia l in te rs e c ts th e u p p e r level of th e S c h u m a n n —R u n g e sy s te m a t a low v ib ra tio n a l lev el (v'=2). T h is will h a v e a d ire c t c o n seq u e n ce on th e e m iss io n e m a n a tin g fro m th e s e levels. The firs t positive system of N 2 h a s two such p o ten tials, 5X an d 7£ b u t th e ir effect on th e overall em ission is s u b s ta n tia lly less th a n t h a t in 0 2 as th e y in te rs e c t th e u p p e r levels a t su b s ta n tia lly h ig h e r v ib ratio n a l s ta te s (v'>12). S im ila rly , th e ß b a n d in NO h a s th e 2L re p u lsiv e s ta te w hich in te rs e c ts th e B 2n level, b u t a t th e in te rse c tio n p o in t a t v'= 7 , th e effects on th e o v e ra ll e m iss io n co m in g fro m th is lev e l is, a g a in , co m p a rativ ely sm all.
T he co n clu sio n s d ra w n from th e fo reg o in g d isc u ssio n on io n is a tio n a n d e m issiv itie s a re t h a t th e d o m in a n t io n isin g re a c tio n s a ro u n d th e
N( S)+N ( P)
N( S)+N( D)
N( S)+N( S)
I n te r n u c le a r d is ta n c e r(Ä)
F igure 2.2 +