State-to-state photodissociation dynamics of CO₂ at 157 nm

Abstract

State-to-state photodissociation of CO2(v2=0 and 1) at 157 nm via the O(1D) + CO(X1Σ+) channel was studied by using the sliced velocity map imaging technique. Both the O(1D) and CO(X1Σ+)...

Wavelength-Dependent Dynamics of the O(1D2) Channel in the 1Δu State Photodissociation of CO2

“…Therefore, the initially excited CO 2 molecules favor evolving along O–C–O bending angle from the FC region to the bent equilibria. The dramatic change of the O–C–O bending angle and substantial extension of C–O bond during dissociation on the bend 2 1 A′ PFS will result in a high fraction of CO rotational excitations, as shown in the previous studies of CO 2 dissociation at 157 and 155 nm. − However, the barrier located ∼0.4 eV below the FC point is only about 0.2 eV high, and thus the contribution of direct dissociation through the linear 2 1 A′ state will certainly grow with increasing photon energy. It is reasonable that the linear dissociation path results in little rotational excitations of the products.…”

“…In the case of the direct dissociation of a diatomic molecule in the axial recoil limit, β has limiting values of 2 (for a pure parallel transition) and −1 (for a pure perpendicular transition). According to previous studies, the effect of atomic angular momentum alignment exists in the O( 1 D 2 ) channel resulting from CO 2 photodissociation at 157 and 155 nm. , The alignment effect maybe still present in the region of 143.53–153.03 nm and will have a slight influence on the β values of the photofragments as seen in ref . Therefore, the product angular distributions derived from Figure are analyzed using the following equation instead of eq I ( θ ) = ( 1 / 4 π ) [ 1 + β k P k false( cos nobreak0em0.25em⁡ θ false) ] where β k is the k th-order image anisotropy parameters, P k (cos θ) is the k th-order Legendre polynomials, and k represents a series of even numbers in the case of linearly polarized light.…”

“…As for the observed variation of the β 2 parameters, several origins have been suggested to predict the trend of rotational-state-dependent spatial anisotropy in the previous studies of numerous triatomic molecular systems. ,− In the case of NO 2 , Reisler and co-workers described a semiclassical nonaxial recoil model based on the conservation of energy and angular momentum to explain the deviation of β from the limiting values for the high rotational states . This model was also used in two later studies of photodissociation of OCS done by Lee et al and Brouard et al More recently, the nonaxial recoil effect was considered first in the case of CO 2 photodissociation at 157 and 155 nm to successfully reproduce the general trends of decreasing β as a function of increasing rotational state. , In this study, the CO 2 dissociation in the region of 143.53–153.03 nm also mainly occurs with the transition dipole moment in the bent CO 2 molecular plane, resulting in high rotational excitation of the CO photofragments. Thus, it is appropriate to explain the ro-vibrational-state-dependent attenuation of β 2 parameters with the consideration of the nonaxial recoil effect.…”

“…Even so, the trend of ro-vibrational-statedependent β 2 follows the trend of spatial anisotropy according to the previous studies. 15,16 Therefore, the lower ro-vibrationally excited CO products obtained at 143.53 and 153.03 nm seem to have relatively higher spatial anisotropy parameters.…”

“…Different from those of both early studies, the anisotropy parameter for the O( 1 D 2 ) channel was found to depend on the translational energy. Very recently, Zhang et al 15 used the sliced velocity map imaging technique with (2 + 1) resonance enhanced multiphoton ionization (REMPI) to determine the j-dependent anisotropy parameters for the CO(v = 0 and 1, j) photoproducts from photodissociation of CO 2 (v 2 = 0 and 1).…”