Nonlinear X-wave formation and conical emission at different powers of a femtosecond laser pulse in water

Nonlinear X-wave formation at different pulse powers in water is simulated using the standard model of nonlinear Schrödinger equation (NLSE). It is shown that in near field X-shape originally emerges from the interplay between radial diffraction and optical Kerr effect. At relatively low power group-velocity dispersion (GVD) arrests the collapse and leads to pulse splitting on axis. With high enough power, multi-photon ionization (MPI) and multi-photon absorption (MPA) play great importance in arresting the collapse. The tailing part of pulse is first defocused by MPI and then refocuses. Pulse splitting on axis is a manifestation of this process. Double X-wave forms when the split sub-pulses are self-focusing. In the far field, the character of the central X structure of conical emission (CE) is directly related to the single or double X-shape in the near field.     

On the Circuit-cocircuit Intersection Conjecture

Oxley has conjectured that for k≥4, if a matroid M has a k-element set that is the intersection of a circuit and a cocircuit, then M has a (k−2)-element set that is the intersection of a circuit and a cocircuit. In this paper we prove a stronger version of this conjecture for regular matroids. We also show that the stronger result does not hold for binary matroids. The second author was partially supported by CNPq (grant no 302195/02-5) and the ProNEx/CNPq (grant no 664107/97-4).     

On the aspect of plane of appearance of Jahn-Teller and Renner-Teller intersections in tetra-atomic system—A case study with HCNO+

A search for configuration space with well-defined topological (Berry) phases corresponding to Jahn-Teller (JT) conical intersection (CI) and Renner-Teller (RT) parabolic intersection (PI) in the linear tetra-atomic molecular system on introduction of bending demonstrates the interesting aspect that these potential intersections may appear in the molecular plane as well as out of the molecular plane. While understanding this aspect is important for following the class of phenomena led by potential intersections, till date, studies on molecular systems, including pairs such as (C₂H₂⁺, HCNH) and (N₂H₂⁺, HBNH⁺), have not been able to clarify the issue. The present article includes calculation of nonadiabatic coupling terms involving four low-lying states of slightly bent HCNO⁺, a motivated choice of tetra-atomic with all four different atoms, to study this aspect associated with JT-CI and RT-PI in a slightly bent linear system. The plane of appearance of these effects has been advocated to be related to the electronic configuration of the concerned states of the molecular system.     

State Selectivity and Dynamics in Dissociative Electron Attachment to CF3I Revealed through Velocity Slice Imaging

In light of its substantially more environmentally friendly nature, CF₃I is currently being considered as a replacement for the highly potent global‐warming gas CF₄, which is used extensively in plasma processing. In this context, we have studied the electron‐driven dissociation of CF₃I to form CF₃^? and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron‐driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the ²P_1/2 excited state of iodine, electron‐induced dissociation leads predominantly to the ²P_3/2 ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process.     

Conical Intersections and Low‐Lying Electronic States of Tetrafluoroethylene

The low‐lying electronic states of tetrafluoroethylene (C₂F₄) are characterized theoretically for the first time using equation‐of‐motion coupled cluster theory (EOM‐CCSD), and complete active space self‐consistent field (CASSCF) and second‐order perturbation theory (CASPT2). Computations are performed for vertical excitation energies, equilibrium geometries, minimum‐energy conical intersections, and potential energy curves along three geometric coordinates: 1) twisting of the F?C?C?F dihedral angle, 2) pyramidalization of the CF₂ group, and 3) migration of a fluorine atom resulting in an ethylidene‐like (CF₃CF) structure. The results suggest two relaxation pathways from the Rydberg‐3s excited electronic state to the ground state. These relaxation pathways are discussed in conjunction with the femtosecond photoionization spectroscopy results of Trushin et al. [ChemPhysChem­ 2004 , 5, 1389].     

不同初始振动态下D2O在B带的态-态光解动力学

利用高精度的非绝热从头算势能面,采用量子实波包方法研究了D₂O在3个不同初始振动态(0,1,0)、(1,0,0)和(0,0,1)下光激发到~B态解离过程的态-态量子动力学．结果表明,由于初始振动波函数的形状不同,从不同振动态产生的吸收光谱、产物分布和产物分支比具有不同的动力学特性．弯曲振动态(010)的吸收谱呈现出两波瓣的形状且中间具有较浅的极小值,其基态产物OD( ~X)在高能量区域会出现轻微的振动态反转现象．所有初始振动态得到的激发态产物OD(_?)的振-转态分布都随能量的变化出现强烈的震荡,这是由于受到了激发态势能面上长寿命共振态的影响．反对称伸缩振动态(0,0,1)在高能量区域具有较大的产物分支比OD(_?)/OD( ~X),表明绝热通道在某些情形下是主要的解离通道．     

Ultrafast Dynamics of the Transoid-cis Isomer Formed in Photochromic Reaction from 3H-Naphthopyran

Recent efforts in designing new 3H-naphthopyran derivatives have been focused on efficient coloration process with a short fading time of the colored transoid-cis TC isomer. It is desirable to avoid photoisomerization of TC leading to transoid-trans TT isomers in the photoreaction. Long lifetime of TT can hamper fast applications such as dynamic holographic materials and molecular actuators, the residual color is one of the serious issues for photochromic lenses. Herein we characterize the photophysical and photochemical channels of TC excited state deactivation competing with the unwanted TC → TT isomerization process. Transient absorption spectroscopy reveals a very short lifetime of the singlet excited TC (≈0.8 ps) and its deactivation channels as S₁→S₀ internal conversion (major), intersystem crossing S₁→T₁, pyran ring formation, photoenolization and TC → TT isomerization. Computations support the S₁→S₀ and T₁→S₀ channels as responsible for photostabilization of the TC form.     

A Photoinduced Nonadiabatic Decay-Guided Molecular Motor Triggers Effective Photothermal Conversion for Cancer Therapy

It remains highly challenging to identify small molecule-based photothermal agents with a high photothermal conversion efficiency (PTCE). Herein, we adopt a double bond-based molecular motor concept to develop a new class of small photothermal agents to break the current design bottleneck. As the double-bond is twisted by strong twisted intramolecular charge transfer (TICT) upon irradiation, the excited agents can deactivate non-radiatively through the conical intersection (CI) of internal conversion, which is called photoinduced nonadiabatic decay. Such agents possess a high PTCE of 90.0 %, facilitating low-temperature photothermal therapy in the presence of a heat shock protein 70 inhibitor. In addition, the behavior and mechanism of NIR laser-triggered molecular motions for generating heat through the CI pathway have been further understood through theoretical and experimental evidence, providing a design principle for highly efficient photothermal and photoacoustic agents.     

Functional and Basis Set Dependence for Time-Dependent Density Functional Theory Trajectory Surface Hopping Molecular Dynamics: Cis-Azobenzene Photoisomerization

Within three functionals (TD-B3LYP, TD-BHandHLYP, and TD-CAM-B3LYP) in combination with four basis sets (3-21g, 6-31g, 6-31g(d), and cc-pvdz), global switching (GS) trajectory surface hopping molecular dynamics has been performed for cis-to-trans azobenzene photoisomerization up to the S₁(nπ*) excitation. Although all the combinations show artificial double-cone structure of conical intersection between ground and first excited states, simulated quantum yields and lifetimes are in good agreement with one another; 0.6 (±5%) and 40.5 fs (±10%) by TD-B3LYP, 0.5 (±10%) and 35.5 fs (±4%) by TD-BHandHLYP, and 0.44 (±9%) and 35.2 fs (±10%) by TD-CAM-B3LYP. By analyzing distributions of excited-state population decays, hopping spots, and typical trajectories with performance of 12 functional/basis set combinations, it has been concluded that functional dependence for given basis set is slightly more sensitive than basis set dependence for given functional. The present GS on-the-fly time-dependent density functional theory (TDDFT) trajectory surface hopping simulation can provide practical benchmark guidelines for conical intersection driven excited-state molecular dynamics simulation involving in large complex system within ordinary TDDFT framework. © 2019 Wiley Periodicals, Inc.