Angle-dependent strong-field ionization of triple bonded systems calculated by time-dependent configuration interaction with an absorbing potential

Abstract

The angle dependence of strong field ionization has been studied for a set of molecules containing triple bonds: HCCH, HCN, HCC–CN, H2N–CCH, H2N–CN, and H2N–CC–CN. Time-dependent configuration interaction (TDCI) with a complex absorbing potential was used to model strong field ionization by a linearly polarized seven-cycle 800 nm cosine squared pulse. The ionization yields have been calculated as a function of the laser intensity and polarization direction and plotted as three-dimensional surfaces. At low field strengths, the angular dependence can be understood in terms of ionization from the highest occupied orbitals. At higher laser intensities, ionization occurs from lower lying orbitals as well as from the highest occupied orbitals, as indicated by changes in the angular dependence of the ionization yield and by variations in the population analysis of the TDCI wavefunction with the intensity of the laser field. The ionization yield for directions parallel to the molecular axis increases more rapidly than perpendicular to the axis as the conjugation length is increased. NH2 substitution substantially increases the ionization yield along the molecular axis but has only a small effect for perpendicular directions.

Angular Dependence of Strong Field Ionization of CH3X (X = F, Cl, Br, or I) Using Time-Dependent Configuration Interaction with an Absorbing Potential

“…For simulations of strong field ionization with the TDCIS-CAP approach, standard basis sets need to be augmented with several sets of diffuse functions to describe the electron as it is propagated from the valence region over the Coulomb barrier toward the absorbing boundary. In previous work, we developed an absorbing basis and tested it on various small molecules, first row hydrides, and molecules containing multiple bonds. − As the halogen in CH 3 X is changed from X = F to I, the electrons in the frontier orbitals are more easily ionized, and a larger absorbing basis may be needed in the ionization simulations. Table lists the exponents of the diffuse uncontracted Gaussian functions that we used for first row systems (basis A) along with two larger basis sets with more diffuse functions (basis B and basis C).…”

“…In previous studies, we examined the angular dependence of strong field ionization of several small molecules, first and second row hydrides, and various molecules with multiple bonds. − We used time dependent configuration interaction with a complex absorbing potential (TDCIS-CAP) to simulate ionization by short, intense 800 nm pulses. The angle dependence can be readily interpreted in terms of the highest occupied molecular orbitals.…”

Angular Dependence of Strong Field Ionization of 2-Phenylethyl-N,N-dimethylamine (PENNA) Using Time-Dependent Configuration Interaction with an Absorbing Potential

“…For sufficiently strong fields, ionization can occur by tunneling through the Coulomb barrier or by barrier suppression. In previous studies we have used time-dependent configuration interaction with a complex absorbing potential (TDCI-CAP) to simulate strong field ionization. − This has revealed a strong angular dependence for the ionization rate. For small, high symmetry molecules, the shape of the frontier orbitals dictates the angular dependence of ionization.…”

Angular Dependence of Strong Field Ionization of Haloacetylenes HCCX (X = F, Cl, Br, I), Using Time-Dependent Configuration Interaction with an Absorbing Potential

“…For ionization in the tunneling regime, a better description can be obtained using molecular Ammosov–Delone–Krainov (ADK) theory. , Solving the time-dependent Schrödinger equation (TDSE) provides a more quantitative description of angular dependence of ionization and HHG spectra. The TDSE can be solved utilizing approximations such as single active electron, quantitative rescattering theory, time-dependent resolution in ionic states, time-dependent analytical R-matrix, and time dependent generalized active space configuration interaction. − In previous studies, we examined the angle dependence of various small molecules using a time-dependent configuration interaction (TDCI) approach with a complex absorbing potential (CAP). − In addition to a standard molecular basis, like aug-cc-pVTZ, the TDCI-CAP calculations need a large number of diffuse functions (which we termed the absorbing basis) to describe the electron density between the valence region and the complex absorbing potential (CAP). A larger absorbing basis is needed for heavier elements, and this was developed using the methyl halides as a test case …”