REMPI-TOF studies of the translational anisotropy and the polarization of the O (1D2) photofragment angular momentum following ozone photolysis at 298 nm

Abstract

The translational anisotropy and the polarization of the electronic angular momentum of the O ((1)D2) fragment produced from the 298 nm photodissociation of ozone have been determined using resonance enhanced multiphoton ionization (REMPI) in conjunction with time-of-flight mass spectrometry (TOFMS). The translational anisotropy parameter beta, which is necessarily averaged over the O2 co-fragment rotational distribution, is measured to be 1.08 +/- 0.04. This is consistent with that expected for the (1)B2 <-- (1)A1 transition within an impulsive model if the tangential velocity associated with the zero point motion of the bend is constricted to opening the bond angle. Molecular frame polarization parameters of rank up to k = 4 have been extracted for the O ((1)D2) fragment and the calculated m(J) populations show a strong preference for the absolute value(m(J)) = 1 states. A small coherence term is also observed, a manifestation of the nuclear geometry of the dissociating molecule and the existence of possible non-adiabatic processes in the exit channel. The orientation associated with the mapping of the photon helicity onto the O ((1)D2) electronic angular momentum distribution was observed to have been quenched. However, the parameter gamma1', which describes the contribution to the orientation from a coherent superposition of a parallel and perpendicular excitation where the photofragment angular momentum lies perpendicular to both the recoil velocity and to the transition dipole moment, was determined to be -0.06.

The photodissociation dynamics of ozone at 193nm: An O(D21) angular momentum polarization study

“…I B, an experimental study of the orientation of O (1D 2) subsequent to excitation into the Hartley band at wavelengths between 248 and 285 nm has 23 recently been undertaken by Lee et al These experiments revealed a significant, speed-dependent y 1 ' parameter, which on average is about a factor of 10 higher than we observe at 193 nm but is of the same sign. The newer work at 298 nm by Denzer et al 25 yields a similar y1 parameter to those 23 obtained by Lee et al, if the latter are averaged over recoil speed. Furthermore, once the y 1 ' parameters are transformed into the molecular frame, they also agree well with the pre dicted orientation generated from the state of 1A symmetry at linearity that we have derived above from the long range model.…”

Photodissociation dynamics of OCS at 248nm: The S(D21) atomic angular momentum polarization

“…The velocity-averaged values of Im͓a 1 1 ͑ ʈ , Ќ ͔͒ obtained here at 248 nm are similar in magnitude to those observed by Lee et al at 193 nm. 26,28,42,60,61 With one exception, 28 these studies returned zero 42,60 or small 26 values for the in-plane orientation moments. In the past, the possibility of static coherence arising from excitation to the 2 1 AЈ surface was discounted on the basis of the small perpendicular projection of the transition dipole moment on the recoil axis.…”

Origin of the “odd” behavior in the ultraviolet photochemistry of ozone

“…ozone | photochemistry | quantum dynamics | isotopic fractionation | lambda doublets G iven the importance of the stratospheric ozone layer in protecting the earth from harmful ultraviolet (UV) rays (1), it is not surprising that the UV photodissociation of ozone has been the subject of numerous experimental (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) and theoretical studies (16)(17)(18)(19)(20)(21)(22)(23)(24). In the strongly absorbing Hartley band (200-300 nm), the photodissociation involves two low-lying excited states with the same symmetry (A′) as the ground state (X): the B state which diabatically correlates to O 2 (a 1 Δ g ) and O( 1 D) products, and the R state which diabatically correlates to O 2 (X 3 Σ − g ) and O( 3 P) products.…”