Nonequilibrium product distributions observed in the multiple collision chemiluminescent reaction of Sc with NO2. Perturbations, rapid energy transfer routes and evidence for a lowhyphen;lying reservoir state

摘要

Nitrogen dioxide reacts with scandium to yield theBthinsp;2Sgr;+ndash;Xthinsp;2Sgr;+spectrum of ScO. This reaction has been characterized from 10minus;5to 1 Torr in order to study relaxation and rapid intramolecularEndash;Etransfer among ScO excited states. At the lowest pressures, a ground state metal atom interacts with a tenuous atmosphere of oxidant gas (beamhyphen;gas configuration). These rsquo;rsquo;single collisionrsquo;rsquo; studies are extended in a controlled manner to higher pressure by entraining the metal atoms in argon and subsequently carrying out the oxidation of this mixture. At all pressures, the measuredBthinsp;2Sgr;+vibrational populations follow a markedly nonhyphen;Boltzmann distribution. At the lowest pressures, the formation of ScOBthinsp;2Sgr;+results directly from the reaction Sc+NO2rarr;ScOast;+NO. At higher pressures, theBthinsp;2Sgr;+state is also populated via rapid intramolecular energy transfer from longhyphen;lived, weakly emitting rsquo;rsquo;reservoirrsquo;rsquo; states via the sequence Sc+NO2+Arrarr;ScO(res)+NO+Ar and ScO(res)+Arrarr;ScO(Bthinsp;2Sgr;+)+Ar. Spin orbit and Coriolis interactions in ScO connect rovibronic levels ofBthinsp;2Sgr;+and lowhyphen;lying4Pgr;ror2Pgr;ireservoir states resulting in the observation of substantial perturbations inBthinsp;2Sgr;+. Collisional energy transfer is particularly efficient for the most strongly perturbed levels of theB2Sgr;+state. This energy transfer is manifest by the appearance of rsquo;rsquo;extrarsquo;rsquo; band heads representing normally forbidden (small electronic transition moment or Franckndash;Condon factor) rsquo;rsquo;reservoir statersquo;rsquo;ndash; ground state transitions which become allowed because of a small admixture ofBthinsp;2Sgr;+character. The relative intensities of the extra and rsquo;rsquo;mainrsquo;rsquo;Bthinsp;2Sgr;+ndash;Xthinsp;2Sgr;+transitions are strongly dependent on argon buffer gas pressure. A quantitative description of this dependence gives an estimate for the amount of mixing between the reservoir state andBthinsp;2Sgr;+and for the rate of energy transfer between these two states.CollisionaltransfertoScOBthinsp;2Sgr;+vprime;=3ndash;9sfound to proceed at rates which for certain levels approach 100 times gas kinetic. The effects observed in ScO demonstrate that the excited states of this molecule interact in the presence of a collision partner as if they were large diffuse entities. These effects are not pathological. This behavior may have important implications for the modeling of energy systems as well as the ability to create population inversions requisite for the construction of visible chemical laser systems.