Simultaneous Measurement of Reactive and Inelastic Scattering: Differential Cross Section of the H + HD → HD(v′, j′) + H Reaction

Abstract

The H + HD → HD(ν , j ) + H reaction has been studied experimentally and theoretically. Differential cross sections of HD(ν , j ) products have been measured by means of a Photoloc technique and calculated using a time-independent quantum mechanical theory. Three product states: HD(ν = 1, j = 8) at a collision energy (E coll ) of 1.97 eV; HD(ν = 2, j = 3) at E coll = 1.46 eV; and HD(ν = 2, j = 5) at E coll = 1.44 eV, show very good agreement between theory and experiment. The other two, highly rotationally excited states studied, HD(ν = 1, j = 12) and HD(ν = 1, j = 13) at E coll = 1.97 eV, exhibit a noticeable disagreement between experiment and theory. This is consistent with our most recent findings on the H + D 2 → HD(ν , j ) + D reaction, wherein the differential cross sections of HD(ν = 1, high j ) product states showed similar disagreement between the experiment and theory [J. Jankunas, M. Sneha, R. N. Zare, F. Bouakline, and S. C. Althorpe, J. Chem. Phys. 138 (2013) 094310]. In all five cases, however, we find overwhelming support that the experimental signal is a sum of reactive and inelastic scattering events. The interference term escapes detection, frustrating our attempt to observe geometric phase effects. Nevertheless, this work constitutes a first experimental example in which the indistinguishability of reactive and inelastic channels must be taken into account explicitly when constructing differential cross sections.

Geometric phase effects in the ultracold D + HD $ \rightarrow $ D + HD and D + HD $\leftrightarrow $ H + D2reactions

“…GP effects in molecular spectra have been reported in several theoretical treatments [4,12,[28][29][30][31][32][33][34][35][36][37][38] and it has been confirmed experimentally for the molecules Cu 3 , [39] Li 3 , [40] and Na 3 [41]. In stark contrast, the experimental measurement of a GP effect in molecular scattering has continued to be elusive to this day [42,43]. The first theoretical prediction of a GP effect in scattering was made by Mead for the H + H 2 system [44].…”

“…At energies above the conical intersection, large GP effects on the DCSs were reported which give rise to broader bimodal features [61][62][63]. Unfortunately, a recent experimental effort was unable to resolve the GP oscillations in the DCSs for the H + HD  H + HD reaction at energies below the conical intersection [42,43]. No significant GP effects have been reported in the integral cross sections (or reaction rate coefficients) at any thermal energy.…”

Nonadiabatic Ultracold Quantum Reactive Scattering of Hydrogen with Vibrationally Excited HD(v = 5–9)

“…Of particular interest in the present study is the role of the geometric phase (GP) associated with the D 3 h conical intersection (CI) in H 3 . − For thermal scattering at total energies below 1.8 eV, many partial waves contribute and the GP effects all but wash-out in the partial wave sum for both the integral and differential cross sections. ,− However, for thermal scattering at higher total energies above 1.8 eV but below the energy of the CI (∼2.7 eV), some small GP effects were finally reported in the differential cross sections (DCSs) by Juanes-Marcos and Althorpe . Additional theoretical studies at energies above the CI reported large GP effects, which lead to bimodal features in the DCSs. − An experimental attempt to resolve the theoretically reported GP induced oscillations in the DCSs for the H + HD → H + HD reaction at energies below the CI was unsuccessful. , However, a recent high-resolution experiment finally measured the GP effect for the first time in the DCSs for the H + HD → H 2 + D reaction at a collision energy of 2.77 eV (total energy 2.99 eV) . Interference effects due to the GP give rise to a peak at zero scattering angle (forward scattering).…”

Differential Cross Sections for the H + D2 → HD(v′ = 3, j′ = 4–10) + D Reaction above the Conical Intersection

“…A least-squares fitting procedure , was performed to compare the theoretical calculations with experimental measurements. The fitting parameter R 2 value is used to quantify the quality of the fitting process and to provide a measure of how well the theoretical DCSs agree with the experimental ones. A value of R 2 = 1 represents a perfect agreement.…”

“…The theoretically calculated DCSs have been modified to simulate the experimental conditions as described above in Slow-Channel Correction (see Figure ) and presented in Figure using solid black lines. A least-squares fitting procedure , was performed to compare the theoretical calculations with experimental measurements. The fitting parameter R 2 value is used to quantify the quality of the fitting process and to provide a measure of how well the theoretical DCSs agree with the experimental ones.…”