Oscillation of Branching Ratios Between the D(2s)+D(1s) and the D(2p)+D(1s) Channels in Direct Photodissociation of D_{2}

Spectra and Predissociation Dynamics of the 4pσB''1∑u+ and 4pπD' 1Πu States of D2

The spectra and predissociation dynamics of the Rydberg states 4pσB″1∑u+(υ'=2) and 4pπD'1Πu±(υ'=1) of the D2 molecule have been studied by a combination of XUV laser pump, UV laser probe, and velocity map imaging methods. The D(2l) fragment yield spectrum and the D2 excitation spectrum have been measured. Although the predissociation rates were found to be small and comparable to the radiative decay rates, the D(2l) fragments were observed for all the Rydberg states. The measured D(2l) fragment angular distributions are in good agreement with a reported model that has an analytical formula for anisotropy parameters. The results demonstrated that the 4pσB″1∑u+ and 4pπD'1Π u+ states dissociate via direct and indirect coupling with an 1∑u+ state, respectively. For predissociation of the 4pσB″1∑u+ state, the experimental data showed that D(1s) + D(2s) is the main channel, supporting previous theoretical predictions that the predissociation occurs by coupling to the vibrational continuum of the 3pσB'1∑u+ state.

Photodissociation of HCl in the photon energy range 14.6-15.0 eV: Channel-resolved branching ratios and fragment angular distributions

For the HCl molecule, four photodissociation channels are open in the excitation energy region 14.6-15.0 eV: H(2s) + Cl(²P_3/2), H(2p) + Cl(²P_3/2), H(2s) + Cl(²P_1/2), and H(2p) + Cl(²P_1/2). We measured the fragment angular distributions and the branching ratios of the four dissociation channels by using the extreme ultraviolet laser pump and UV laser probe, delay-time-curve, and velocity map imaging methods. The channel-resolved fragment angular distributions and fragment yield spectra show that various Rydberg states (superexcited states) contribute to the absorption cross sections, including the [A²Σ⁺]4pσ, [A²Σ⁺]4pπ, [A²Σ⁺]3dσ, [A²Σ⁺]3dπ, and [A²Σ⁺]5sσ states. Most of the H(2s) + Cl(²P_1/2) channels correlate with the ¹Σ⁺ states, while the other channels correlate with mixing excitations of the ¹Σ⁺ and ^1,3Π states. The channel branching ratios are dependent on the excitation energies. When the four channels are open, the channel branching ratios of H(2s) + Cl(²P_3/2) and H(2p) + Cl(²P_1/2) are small. Based on the recent ab initio potential energy curves, the Rydberg states converging to the ion-core A²Σ⁺ are proposed to be predissociated by the nuclear vibrational continua of the Rydberg states converging to the ion-core X²Π.