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The above-threshold ionization process of ammonia molecules induced by a femtosecond laser field at 800 nm is studied in the intensity range from 1.6 Ă— 1013 to 5.7 Ă— 1013 W/cm2. Channel switching under different laser intensities is observed and identified in the photoelectron kinetic energy spectra of ammonia. Based on the photoelectron kinetic energy distributions and the photoelectron angular distributions, the characteristic peaks observed are exclusively assigned to the multiphoton resonance through certain intermediate states, followed by multiphoton above-threshold ionization. [ABSTRACT FROM AUTHOR]

Based on the first-principles method, we predict two new stable BN allotropes: C12-BN and O16-BN, which belong to cubic and orthorhombic crystal systems, respectively. It is confirmed that both the phases are thermally and dynamically stable. The results of molecular dynamics simulations suggest that both the BN phases are highly stable even at high temperatures of 1000 K. In the case of mechanical properties, C12-BN has a bulk modulus of 359 GPa and a hardness of 43.4 GPa, making it a novel superhard material with potential technological and industrial applications. Electronic band calculations reveal that both C12-BN and O16-BN are insulators with direct band gaps of 3.02 eV and 3.54 eV, respectively. The XRD spectra of C12-BN and O16-BN are also simulated to provide more information for possible experimental observation. Our findings enrich the BN allotrope family and are expected to stimulate further experimental interest. [ABSTRACT FROM AUTHOR]

We report the structure and physical properties of two newly discovered compounds AV8Sb12 and AV6Sb6 (A = Cs, Rb), which have C 2 (space group: Cmmm) and C 3 (space group: R 3 ÂŻ m) symmetry, respectively. The basic V-kagome unit appears in both compounds, but stacking differently. A V2Sb2 layer is sandwiched between two V3Sb5 layers in AV8Sb12, altering the V-kagome lattice and lowering the symmetry of kagome layer from hexagonal to orthorhombic. In AV6Sb6, the building block is a more complex slab made up of two half-V3Sb5 layers that are intercalated by Cs cations along the c -axis. Transport property measurements demonstrate that both compounds are nonmagnetic metals, with carrier concentrations at around 1021 cmâˆ'3. No superconductivity has been observed in CsV8Sb12 above 0.3 K under in situ pressure up to 46 GPa. Compared to CsV3Sb5, theoretical calculations and angle-resolved photoemission spectroscopy reveal a quasi-two-dimensional electronic structure in CsV8Sb12 with C 2 symmetry and no van Hove singularities near the Fermi level. Our findings will stimulate more research into V-based kagome quantum materials. [ABSTRACT FROM AUTHOR]