Vibrational states of the triplet electronic state of H3+. The role of non-adiabatic coupling and geometrical phase

Vibrational energies and wave functions of the triplet state of the H3+ ion have been determined. In the calculations, the ground and first excited triplet electronic states are included as well as the non-Born-Oppenheimer coupling between them. A diabatization procedure transforming the two adiabatic ab initio potential energy surfaces of the triplet-H3+ state into a 2x2 matrix is employed. The diabatization takes into account the non-Born-Oppenheimer coupling and the effect of the geometrical phase due to the conical intersection between the two adiabatic potential surfaces. The results are compared to the calculation involving only the lowest adiabatic potential energy surface of the triplet-H3+ ion and neglecting the geometrical phase. The energy difference between results with and without the non-adiabatic coupling and the geometrical phase is about a wave number for the lowest vibrational levels

Photofragmentation of the H_3 molecule, including Jahn-Teller coupling effects

We have developed a theoretical method for interpretation of photoionization experiments with the H_3 molecule. In the present study we give a detailed description of the method, which combines multichannel quantum defect theory, the adiabatic hyperspherical approach, and the techniques of outgoing Siegert pseudostates. The present method accounts for vibrational and rotation excitations of the molecule, deals with all symmetry restrictions imposed by the geometry of the molecule, including vibrational, rotational, electronic and nuclear spin symmetries. The method was recently applied to treat dissociative recombination of the H_3^+ ion. Since H_3^+ dissociative recombination has been a controversial problem, the present study also allows us to test the method on the process of photoionization, which is understood better than dissociative recombination. Good agreement with two photoionization experiments is obtained.Comment: 10 figure

Calculation of three-body resonances using slow-variable discretization coupled with complex absorbing potential

We developed a method to calculate positions and widths of three-body resonances. The method combines the hyperspherical adiabatic approach, slow variable discretization method (Tolstikhin et al., J. Phys. B: At. Mol. Opt. Phys. 29, L389 (1996)), and a complex absorbing potential. The method can be used to obtain resonances having short-range or long-range wave functions. In particular, we applied the method to obtain very shallow three-body Efimov resonances for a model system (Nielsen et al., Phys. Rev. A 66, 012705 (2002)).Comment: 23 pages, 10 figure

Geometrical phase driven predissociation: Lifetimes of 2^2 A' levels of H_3

We discuss the role of the geometrical phase in predissociation dynamics of vibrational states near a conical intersection of two electronic potential surfaces of a D_{3h} molecule. For quantitative description of the predissociation driven by the coupling near a conical intersection, we developed a method for calculating lifetimes and positions of vibrational predissociated states (Feshbach resonances) for X_3 molecule. The method takes into account the two coupled three-body potential energy surfaces, which are degenerate at the intersection. As an example, we apply the method to obtain lifetimes and positions of resonances of predissociated vibrational levels of the 2^2 A' electronic state of the H_3 molecule. The three-body recombination rate coefficient for the H+H+H -> H_2+H process is estimated.Comment: 4 pages, 4 figure

Photofragmentation of the H-3 molecule, including Jahn-Teller coupling effects

We have developed a theoretical method for interpretation of photoionization experiments with the H-3 molecule. In the present study we give a detailed description of the method, which combines multichannel quantum defect theory, the adiabatic hyperspherical approach, and the techniques of outgoing Siegert pseudostates. The present method accounts for vibrational and rotation excitations of the molecule, deals with all symmetry restrictions imposed by the geometry of the molecule, including vibrational, rotational, electronic, and nuclear spin symmetries. The method was recently applied to treat dissociative recombination of the H-3(+) ion. Since H-3(+) dissociative recombination has been a controversial problem, the present study also allows us to test the method on the process of photoionization, which is understood better than dissociative recombination. Good agreement with two photoionization experiments is obtained

Theoretical study of dissociative recombination of C-2v triatomic ions: Application to H2D+ and D2H+

We develop a theoretical treatment of the dissociative recombination of triatomic molecular ions of the C-2v molecular symmetry group. Using the method, we study the dissociative recombination of the H2D+ and D2H+ ions. The theoretical rates obtained for the H2D+ and D2H+ dissociative recombination are in general agreement with storage-ring experiments although there are some potentially informative discrepancies

Radiative electron attachment to rotating C3_3N through dipole-bound states

The role of a large dipole moment in rotating neutral molecules interacting with low-energy electrons is studied using an accurate {\it ab initio} approach accounting for electronic and rotational degrees of freedom. It is found that theory can reproduce weakly-bound (dipole-bound) states observed in a recent photodetachment experiment with C$_3$N$^-$ [Phys. Rev. Lett. {\bf 127}, 043001 (2021)]. Using a similar level of theory, the cross section for radiative electron attachment to the C$_3$N molecule, forming the dipole-bound states, was determined. The obtained cross section is too small to explain the formation of C$_3$N$^-$ in the interstellar medium, suggesting that it is likely formed by a different process

Theory of dissociative recombination of a linear triatomic ion with permanent electric dipole moment: Study of HCO+

We present a theoretical description of dissociative recombination of triatomic molecular ions having large permanent dipole moments. The study has been partly motivated by a discrepancy between experimental and theoretical cross sections for dissociative recombination of the HCO+ ion. The HCO+ ion has a considerable permanent dipole moment (D approximate to 4 D), which has not been taken explicitly into account in previous theoretical studies. In the present study, we include explicitly the effect of the permanent electric dipole on the dynamics of the incident electron using the generalized quantum defect theory, and we present the resulting cross section obtained. This demonstrates the possibility of applying generalized quantum defect theory to the dissociative recombination of molecular ions

Calculation of three-body resonances using slow-variable discretization coupled with a complex absorbing potential

We developed a method to calculate positions and widths of three-body resonances. The method combines the hyperspherical adiabatic approach, slow variable discretization method [O. I. Tolstikhin , J. Phys. B 29, L389 (1996)], and a complex absorbing potential. The method can be used to obtain resonances having short-range or long-range wave functions. In particular, we have applied the method to obtain very shallow three-body Efimov resonances for a model system [E. Nielsen , Phys. Rev. A 66, 012705 (2002)]

Photodetachment cross sections of the C2nH- (n=1-3) hydrocarbon-chain anions

We report theoretical results of the low-energy photodetachment cross sections of the C2H-, C4H-, and C6H- hydrocarbon-chain anions. The complex Kohn variational technique is used to calculate molecular-frame transition dipole moments from the anion ground state to a photoelectron in the continuum of the neutral radical. We employ the Franck-Condon approximation and include interchannel electronic coupling to determine the low-energy photodetachment cross sections and asymmetry parameters. We discuss the behavior of the cross section, especially near thresholds, and describe the role of electronic resonances and excited channels. The theoretical results reproduce the main characteristics of recent measurements of absolute photodetachment cross sections