Attosecond imaging of molecules using high harmonic spectroscopy

Lanczos-based equation-of-motion coupled-cluster singles-and-doubles approach to the total photoionization cross section of valence excited states

“…Reference values computed numerically 50 with experimental rovibronic constants 42 were obtained at 9.92 eV and 9.31 eV for the 1 Σ − u and 1 Π g excited states, respectively. We notice that the EOM-CCSD vertical excitation energies are closer to the reference values 50 than the ones calculated at the ADC (2) and ADC(2)-x levels. 7 Also, our EOM-CCSD adiabatic excitation energies are 8.85 eV for the 1 Σ − u excited state and 8.84 eV for the 1 Π g excited state, versus experimental values of 8.59 and 8.45 eV for the 1 Σ − u and 1 Π g excited states, 42 respectively.…”

“…Mb. This feature is absent in the cross sections obtained both at the ADC (2) and ADC 2-x levels, showing that, for this molecule, the EOM-CCSD cross section is more sensitive to the molecular geometry variations than the ADC curves.…”

“…Our EOM-CCSD photoionization cross sections from the two lowest excited states of water, 1 B 1 and 1 A 2 , are shown in the Figures 2 and 3, respectively, together with the ADC (2) and ADC 2 excited states, respectively, see Table I). Compared to the ADC(2) and ADC 2-x results 7…”

“…With the advent of attosecond light pulses, photons lying in the ultraviolet (UV) and Xray spectral regions can now be employed as the probing light in pump-probe spectroscopy experiments reaching the attosecond time scale. [1][2][3][4][5][6][7][8][9][10][11][12] The development of new experimental techniques to access information on transient states of atoms and molecules asks for Many computational studies of the photoionization/photoabsorption cross-sections of valence and/or core electrons of atoms and molecules in their electronic ground state relying on L 2 basis sets have been reported employing either the well known Stieltjes imaging procedure [13][14][15][16][17][18] or an analytical continued procedure based on the Padé approximants [19][20][21][22] to describe the continuum part of the spectra.…”

Site-specific tunnel-ionization in high harmonic generation in molecules

“…In atomic or molecular gases, it can be described as a three-step process [1,2]: first, near the maxima of the driving field's amplitude, an electronic wavepacket is tunnel-ionized from the parent atom; in the second step, the electronic wavepacket is accelerated and, after reversal of the sign of the electric field, it is redirected to the parent ion; finally, upon recollision, the electron's kinetic energy is emitted in the form of high-frequency radiation. The harmonic spectra encode information of the target structure and dynamics, that can be disentangled using high-harmonic spectroscopy (HHS) and time resolved attosecond spectroscopy techniques [3]. These procedures have been successful in retrieving the information from the HHG spectra about molecular structure [4][5][6], nuclear dynamics [7], molecular orbitals [8,9], energy dispersion in solids [10], dynamics in strongly correlated systems [11], tunneling times [12], and orbital tomography [13][14][15].…”