Quantum Interference Effects Theoretically Found in the Photodissociation Processes of the Second Absorption Bands of ICl and IBr Molecules

Abstract

Some quantum interference effects are exposed directly in experiments, but others are not and remain just hidden and thus require thorough theoretical analysis to be exposed. In this respect, the second absorption bands of IX (X = Cl, Br) molecules show an interesting behavior in the photofragment anisotropy of the lowest I((2)P3/2)+X((2)P3/2) product channel; it changes from strongly parallel distribution on the shorter wavelength side to strongly perpendicular distribution on the longer wavelength side. Because the responsible perpendicular third Ω = 1 (1(III)) excited state correlating adiabatically to this product channel has only a weak absorption, the parallel component flux yielding the same products must be comparatively weak, even though the responsible parallel excitations to the 0(+)(III) and/or 0(+)(IV) excited states have strong absorptions. In the present theoretical study, the branching ratios and the anisotropy parameters have been obtained using the spin-orbit configuration interaction method combined with the quantum mechanical wavepacket and semiclassical approaches. Significant quantum interference effect between the two dissociative de Broglie waves on the 0(+)(III) and 0(+)(IV) potential curves has been found through the avoided crossing, and the weak parallel flux to the ground-state product channel has been explained by their destructive interference character. This interference effect has weak excitation energy dependence due to rather unique behavior of their almost parallel potential curves from the Franck-Condon to avoided crossing regions.

Visualizing coherent vibrational motion in the molecular iodine B3Π0+u state using ultrafast XUV transient-absorption spectroscopy

“…Finally, the upper states, defined in the calculations as two 0 + g states and attributed to the Y 3 S -0 + g and Z 3 0+ g excited states based in particular on Mulliken's work [14] are characterized by a [2341] and a [2422] configuration, respectively. The configuration interaction coefficients as a function of the internuclear distance describing these two states are however strongly mixed as previously observed for IBr and ICl molecules [42] and their configuration is expected to change through avoided crossings and at the asymptotic limit. Thus, both excited states can be described to some extent as a [2341] configuration and their population from the B state is associated with a global  → * excitation.…”

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F1 and F2 spin‐rotation levels of the CN products

“…Then the second unitary transformation distinguishes the ensemble with the F 1 and F 2 components. Of course, the details of the interference pattern are determined by their incoming two probability amplitudes, relative magnitudes and phases, accumulated up to each of the nonadiabatic points during the dissociation, and the structure of the so‐called reduced S ‐matrix …”

“…We have used state‐averaged multi‐configuration self‐consistent field MOs with the weights of 1 Σ + : 3 Π x ( n → σ *): 3 Π y ( n → σ *): 1 Π x ( n → σ *): 1 Π y ( n → σ *): 3 Σ + ( σ → σ *): 3 Σ + ( n → π * ) = 1:3:3:1:1:1.5:1.5 for the FC region ( R < 5.5 bohr) and 1:3:3:1:1:3:0 for the dissociation region ( R > 5.5 bohr), and calculated the adiabatic PESs using the contracted spin–orbit configuration interaction (COSOCI) method as before. For spin–orbit interaction (SOI), we used the one‐electron Breit‐Pauli operator with the effective charges which reproduce the experimental splitting energies of each atom . As the spin‐free states for the COSOCI calculation, we included not only 1 Σ + , 3 Π( n → σ *), 1 Π( n → σ *), 3 Σ + ( σ → σ *) which correlate to the CN(X 2 Σ + ) state but also 3 Σ + ( n → π *), 1,3 Π( π → σ *), 1,3 Δ( n → π *), 1 Σ + ( σ → σ *), 1,3 Σ − ( n → π *) which correlate to the CN(A 2 Π) state.…”

“…As explained above, quantum interference has been vaguely considered as a cause for the N dependence of the f ( N ) . During the past 20 years, in simple molecule photodissociation reactions, it has been established that if wavepackets are simultaneously generated on some PESs by a one‐photon process, quantum interference effects among the dissociating wavepackets appear in various physical quantities of the products such as the angular momentum polarization through nonadiabatic transitions during the dissociation …”

Direct mapping of curve-crossing dynamics in IBr by attosecond transient absorption spectroscopy

“…These trends indicate that the p and p* orbitals are effectively no longer contributing to the variation of the potential energies when the wave packet reaches the avoided crossing. A more direct clue to the electronic-character switching is obtained from the electronic configurations computed for each adiabatic state (36)(37)(38). Just before the avoided crossing, the Bð 3 P 0 þ Þ state is a mixed configuration of [s 2 p 4 p* 3 s* 1 ] and [s 2 p 3 p* 4 s* 1 ]; a single vacancy lies in s*, and the other vacancy is distributed between p and p*.…”