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The metastable hadronic helium atoms in microseconds lifetime are available in laboratory, and two-photon spectroscopy was reported recently. This exotic helium atom has an electron in the ground state and a negative hadron rotating around the helium nucleus. We theoretically study the excitation on hadronic helium by femtosecond pulse and elucidate the influence of moleculelike structure and rotation behavior on the photoelectron spectra and high-order harmonic generation. Because of the moleculelike structure, the electronic ground state consists of several angular orbitals. These angular orbitals can enhance photoelectron spectra at high energies, and also influence the harmonic generation spectra considerably. In particular, the harmonic spectra can occur at even harmonic orders because of the transition between these angular orbitals and continuum states. On the other side, the rotation behavior of hadron can induce a frequency shift in the harmonic spectra. The magnitude of the frequency shift depends on the orbiting speed of the hadron, which is considerable because the rotation period is in a few femtoseconds, a time scale that is comparable to that of infrared laser and is feasible in current laser experiments. [ABSTRACT FROM AUTHOR]

We study high-order harmonic generation (HHG) from the oriented asymmetric molecule HeH2+ and its isotopic variant HeT2+ in strong few-cycle laser pulses, by numerically solving the non-Born-Oppenheimer time-dependent Schrödinger equation. Our simulations show that the influence of nuclear motion on HHG of the asymmetric system is dependent on the molecular orientation and the laser parameters. At relatively weak laser intensities, the HHG yields of HeH2+ are higher than those of HeT2+ for the parallel orientation and the situation reverses for the perpendicular orientation. However, at high laser intensities, they become comparable for the parallel case. With a developed simple HHG model that considers the influences of nuclear motion on all of the ionization, propagation, and recombination processes of HHG, we show the permanent dipole of the system plays an important role in these phenomena. Our results shed light on the complex dynamics of the asymmetric system in strong laser fields. [ABSTRACT FROM AUTHOR]

Variational ab initio R-matrix theory combined with generalized multichannel quantum defect theory is used to calculate singly excited Rydberg states of the hydrohelium molecular ion, HeH+, for 1,3Σ+,1,3Π,1,3Δ,1,3Φ, and 1,3Γ symmetry. Bound levels are calculated for n values up to n≈10, and continuum states up to ≈3 eV above the HeH2+ threshold. The calculations span the range of internuclear distances R from 1 to 5 bohrs. The present work follows a preliminary study on the 1,3Δ states of HeH+ [Bouhali, Bezzaouia, Telmini, and Jungen, EPJ Web Conf. 84, 04004 (2015)] which was also based on R-matrix theory. Further-although limited to rather small R values-the present work extends the recent ab initio computations of Jungen and Jungen [Mol. Phys. 113, 2333 (2015)] to higher excitation energies which are not accessible to standard quantum-chemical methods. Where a comparison with the calculations of Jungen and Jungen and other older results can be made, namely for n≤5, very good agreement with previous ab initio results is obtained. [ABSTRACT FROM AUTHOR]