Picosecond pulse radiolysis study of highly concentrated nitric acid solutions: formation mechanism of NO3• radical.
The formation of nitrate radical, NO(3)(•), is observed for the first time directly by picosecond pulse radiolysis of highly concentrated nitric acid solutions. The experimental yield of NO(3)(-) ionization is deduced from the pulse-probe transient absorption measurements in the visible region where this radical absorbs. On the basis of the value of the extinction coefficient of nitrate radical at 640 nm equal to 1300 M cm(-1), the experimental yield of NO(3)(•) at 20 ps is found to be around 0.36 × 10(-7), 1.33 × 10(-7), and 2.85 × 10(-7) mol J(-1) for 1, 3.5, and 7 M nitric acid solutions, respectively. Relative to the dose absorbed by nitric acid by the direct effect, we find an unexpected high formation yield of the nitrate radical within the electron pulse. Therefore, we suggest that the trapping of the positive hole, H(2)O(•+), by NO(3)(-) also contributes to the formation of NO(3)(•) within the electron pulse. Moreover, after the pulse and within 4 ns, the beginning of the reaction of OH(•) radical with undissociated nitric acid is observed for the most concentrated nitric acid solution.
Laboratoire de Chimie Physique/ELYSE, CNRS/Université Paris-Sud, Faculté des Sciences d'Orsay, Bât. 349, 91405 Orsay Cedex, France.
Anna
A
Balcerzyk
Abdel Karim
AK
El Omar
Uli
U
Schmidhammer
Pascal
P
Pernot
Mehran
M
Mostafavi