Photodissociation Dynamics Of NO₂and CH₃I With Femosecond Pump-Probe Technique

The invention of ion imaging and velocity map imaging has revolutionized ourunderstanding of photodissociation dynamics of molecules. A wide body of literature isavailable now in which a dissociation process is initiated using femtosecond pulsed lasersand the products are detected using ion imaging. The photoexcitation of NO2via the firstexcited state is known to be very complex due to a conical intersection coupling the groundand first excited states. The effect of this conical intersection has been extensively studiedin the frequency and more recently also the time domain. Depending on the typical timescale of the dissociation dynamics, femtosecond pump-probe laser spectroscopy can beused.In this paper, we combine the pump-probe technique and ion imaging velocity mapimaging technique to study the photodissociation dynamics of NO2in femtosecond laser.Finally we have a conclusion that there are three channels:(1) One394nm photon absorption to the A2B2Rydberg state followed by six788nmphoton ionization.(2) Three394nm photon absorption to the52A1Rydberg state followedby three788nm photon ionization.(3) Three394nm photon absorption to thepre-dissociative state followed by three788nm photon ionization.The pre-dissociation dynamics of B Rydberg state of methyl iodide has also been studiedwith femtosecond pump-probe technique. The lifetime of B Rydberg state was determinedto be about1.43ps, which is very consistent with the previous work.Photodissociation dynamics of molecule is an important photochemical process and itis very common in the atmosphere.