Subject: NO2+NO3+M--->N2O5+M

From: <[email-masked]>
Date: Tue, 1 Aug 95 14:41:53+0530

Dear Dr. B.F. Walker: Thank you for your reply.
First  of  all  I  would like to bring  your  attention  that  in 
atmospheric  modeling, researchers consider only the termolecular 
reaction
     NO2 + NO3 + M ------> N2O5 + M          (1)
and not the bimolecular reaction
     NO2 + NO3 ------> N2O5                  (2)
Further, the physical chemistry text books suggest  that 
the  rate constant for the reaction (3) is very much  lower  than 
the reaction (2)
     NO2 + NO3 ------> NO + O2 + NO2         (3),
and -in the stratospheric condition- the atmospheric researchers 
give much importance to the reaction (1) and not the other
dissociation paths. 

Further,  in  1970s  the  reaction  (1)  has  not  received  much 
attention. As a result, the then modeling studies concluded  that 
supersonic  aircraft exhausts (NOx) would  destroy  stratospheric 
ozone  significantly.  This conclusion made a ban  on  supersonic 
aircrafts. Conversely, in recent years it is recognized that  NOx 
would  be  converted  into  N2O5  by  the  reaction  (1)  and  in 
particular very much in the night.  After the 1982 ElChichon  and 
1991 Pinatubo volcanic eruptions, the reaction
     N2O5(g) + H2O (aerosol) ----> 2HNO3 (g)       (4)
is significant in the stratosphere and thus the reactions 1 and 4 
reduced the sensitivity of NOx towards ozone. These conclusions made 
NASA to release High Speed Civil Transport in the near future. Moreover, 
the  current modeling studies consider only the reaction (1)  and 
not the other dissociation paths. (the rate constant values  have 
been used from JPL chemical kinetics and photochemical data).

I  trust I have cleared the importance of the termolecular reaction (1). 
This significance  made  me  to study the  termolecular  reaction  and 
expecting your valuable suggestions. Kindly advice me to  further 
the calculations. Thank you once again.

Sincerely Yours... S. Parthiban

------------------referenced note-------------------------------
I asked:
>Dear Netters:
>We are interested in the rate constant value for the reaction
>          NO2 + NO3 + M ------> N2O5 + M       .....(1)
>and  similar reactions as well, using semi-empirical  method.  To 
>

Dr. B.F. Walker's reply:

The decomposition of N2O5 is usually discussed in undergraduate p chem
classes with the stoichiometry

2N2O5 ----> 4NO2 + O2 

and rate law

r = k[N2O5].

The mechanism is multistep with suggested steps being

N2O5 <----> NO2  +  NO3

NO2  + NO3 -----> NO + O2 + NO2

NO + NO3 ---> 2NO2

Your reaction does NOT require a third body to stabilize the "complex"
molecule N2O5!

Hope this helps.

Ben