Observation of Feshbach-like resonances in collisions between ultracold molecules

We observe magnetically tuned collision resonances for ultracold Cs2 molecules stored in a CO2-laser trap. By magnetically levitating the molecules against gravity, we precisely measure their magnetic moment. We find an avoided level crossing which allows us to transfer the molecules into another state. In the new state, two Feshbach-like collision resonances show up as strong inelastic loss features. We interpret these resonances as being induced by Cs4 bound states near the molecular scattering continuum. The tunability of the interactions between molecules opens up novel applications such as controlled chemical reactions and synthesis of ultracold complex molecules.     

Functional group dependent site specific fragmentation of molecules by low energy electrons

Functional group dependence is observed in the dissociative electron attachment (DEA) to various organic molecules in which the DEA features seen in the precursor molecules of the groups are retained in the bigger molecules. This functional group dependence is seen to lead to site-selective fragmentation of these molecules at the hydrogen sites. The results are explained in terms of the formation of core-excited Feshbach resonances. The results point to a simple way of controlling chemical reactions as well as interpreting the DEA data from bigger biological molecules.     

Modeling of the vibrational structure of the vibronic spectra of diphenylpolyenes by the parametric method

The structures of the electronic-vibrational spectra and of the excited states of a number of diphenylpolyene molecules are determined within the framework of the second approximation of the parametric method. The system of parameters of the structural fragments of molecules is improved and good agreement with spectral experiment is obtained. It is shown that there is a high degree of transferability of the polyene and acene parameters of the method and that the models obtained are adequate to the real structure of molecules. It is also shown that the method proposed makes it possible to perform predictive qualitative and quantitative calculations of the spectra of these molecules, as well as of the spectral characteristics necessary for modeling photochemical molecular transformations. In the series of diphenylpolyene molecules, an interpretation of the vibrational structure of the spectra is proposed and the specific features of variation of the geometry upon excitation of molecules are considered.     

The effect of temperature on urea–urea interactions in water: a molecular dynamics simulation

We investigate the temperature effect on the structural and dynamical properties (translation, rotation) of an urea/water system at 0.20 mole fraction of urea. We report the radial distribution functions of like and unlike molecules and conclude that, even at large distances, these molecules are spatially correlated (with respect to their centers of mass). This behavior is interpreted as an indication that urea molecules are not uniformly distributed at a microscopic level. However, the orientational distribution shows that, at long distances, the urea molecules are not orientationally correlated. A strong correlation between urea molecules is observed within the first-shells of neighboring molecules. In view of these results, it is postulated that urea behaves slightly like a nonpolar molecule. The dynamical properties were analyzed using the velocity (translation) and angular velocity (rotation) time autocorrelation functions, as well as their Fourier transforms. The results indicate a significant hydrogen bonding between urea and other molecules in the solution.     

醇类抑制剂对甲烷水合物形成的影响

在本工作中,甲烷水合物的生长动力学是通过甲醇、乙醇、乙二醇三种不同醇类抑制剂存在下的分子动力学模拟研究的.模拟结果发现,三种醇类都可作为甲烷水合物的抑制剂,醇类分子中的亲水性羟基极大地破坏了水合物笼的结构,并且羟基可以与局部的液态水分子形成氢键,从而增加了形成水合物笼型结构的难度,导致甲烷水合物的生长速率降低.对于甲醇分子,甲醇分子的亲水性羟基与水分子形成氢键从而破坏了水分子结构,而亲油性甲基对周围的水分子具有簇效应,两者都会降低水合物生长速率;对于乙二醇和乙醇分子,它们只含有羟基,特别是乙二醇分子含有两个羟基,其对H₂O分子有很强的吸附作用,导致水合物生长速率降低.在抑制效果方面,甲醇分子最优,乙二醇稍微优于乙醇.     

Collisional stability of fermionic Feshbach molecules

Using a Feshbach resonance, we create ultracold fermionic molecules starting from a Bose-Fermi atom gas mixture. The resulting mixture of atoms and weakly bound molecules provides a rich system for studying few-body collisions because of the variety of atomic collision partners for molecules; either bosonic, fermionic, or distinguishable atoms. Inelastic loss of the molecules near the Feshbach resonance is dramatically affected by the quantum statistics of the colliding particles and the scattering length. In particular, we observe a molecule lifetime as long as 100 ms near the Feshbach resonance.     

Solutions of novel soliton molecules and their interactions of (2 + 1)-dimensional potential Boiti-Leon-Manna-Pempinelli equation

The method of variable separation has always been regarded as a crucial method for solving nonlinear evolution equations. In this paper, we use a new form of variable separation to study novel soliton molecules and their interactions in (2+1)-dimensional potential Boiti-Leon-Manna-Pempinelli equation. Dromion molecules, ring molecules, lump molecules, multi-instantaneous molecules, and their interactions are obtained. Then we draw corresponding images with maple software to study their dynamic behavior.     

Interaction of intense beams of highly vibrationally excited molecules with molecules (clusters) condensed on a cold surface

The interaction of intense beams of SF₆ and CF₃I molecules, excited by powerful IR laser radiation to high vibrational states (0.3 eV ≤ E _vib ≤ 2.0 eV), with molecules (clusters) condensed on a cold surface (T _s ≈ 80–85 K) has been studied. The probability that the excited and unexcited molecules are reflected from the cold metal surface covered by condensed molecules (clusters), as well as the probability that such excited and unexcited molecules are transmitted through a cooled multichannel metal plate and a converging cone oriented at an angle relative to the molecular beam axis, has been determined. Expressions for these probabilities of reflection and transmission as functions of the angle of incidence and the parameters of the exciting laser radiation and the molecular beam are obtained. It is shown that highly vibrationally excited molecules are reflected from the surface and transmitted through the plates and cones with a much higher probability than unexcited molecules. The results suggest that this phenomenon can be used for the separation of molecules in a beam with respect to isotope (or atomic) composition.     

LCI Pariser-Parr-Pople calculations of π-electron systems in nitrogen-heterocyclic molecules. Correlation with spectral data

Limited configuration interaction Pariser-Parr-Pople calculations were performed for 19 nitrogen heterocyclic aromatic molecules. After optimizing the semiempirical parameters for six “test” molecules, calculations were performed for the remaining thirteen molecules. Strong correlations were made with experimentally observed ionization potentials, singlet-singlet transition energies, polarizations and oscillator strengths as well as ground state molecular geometries for cases where these observations have been made. These correlations indicate spectral features which should be carefully examined experimentally to determine the effect of nitrogen substitution in aromatic hydrocarbon molecules.     

Tuneable molecular doping of corrugated graphene

Density functional theory (DFT) modeling of the physisorption of four different types of molecules (toluene, bromine dimmer, water and nitrogen dioxide) over and under graphene ripples has been performed. For all types of molecules changes of charge transfer and binding energies in respect to flat graphene are found. The changes in the electronic structure of corrugated graphene and turn of π-orbitals of carbon atoms in combination with the chemical structure of adsorbed molecules are proposed as the causes of difference with the perfect graphene case and variety of adsorption properties of different types of molecules. The results of calculation suggest that the tops of the ripples are more attractive for large molecules and valley between ripples for small molecules. Stability of molecules on the ripples and energy barriers for migration over flat and corrugated graphene is also discussed.     

乙烷在中孔分子筛MCM-41中吸附的计算机分子模拟

采用计算机模拟方法研究不同温度下乙烷在不同孔径的MCM-41中的吸附.其中乙烷分子采用两个LJ中心的势模型表征，乙烷分子与MCM-41孔壁的相互作用采用一个连续的势模型表示.除考察了温度、孔径对吸附量的影响外，还研究这些量对乙烷分子在孔中的甲基和质心的分布，以及它们对乙烷分子在孔中的排列方向的影响.GCMC模拟结果发现，在180K和300K时壁面处都有较多的乙烷分子倾向于沿着壁面排列，同时在180K时其余的流体分子倾向于垂直于壁面排列，而在300K时其余的分子并不像在180K时一样倾向于垂直于壁面排列.模拟结果还表明，除壁面附近外，即使是在180K的较低温度下，乙烷分子的排列也是混乱和无序的.     

Conductivity of solutions of poly(acrylonitrile) in dimethyl sulfoxide

The conductivity of solutions of poly(acrylonitrile) (PAN) in dimethyl sulfoxide (DMSO) is studied. Using the Raman spectroscopy method, it is found that PAN causes associates of DMSO molecules to dissociate into free molecules, as a result of which the conductivity of the solution grows. Simultaneously, PAN molecules hamper the rotation of DMSO molecules, which decreases the conductivity. There exists a critical concentration of PAN (≈5.4 vol. %) at which the rotation of DMSO molecules is hindered to the greatest extent and the conductivity drops by an order of magnitude.     

Alternate gradient focusing and deceleration of a molecular beam

Neutral dipolar molecules can be decelerated and trapped using time-varying inhomogeneous electric fields. This has been demonstrated only for molecules in low-field seeking states, but can, in principle, be performed on molecules in high-field seeking states as well. Transverse stability is then much more difficult to obtain, however, since molecules in high-field seeking states always experience a force towards the electrodes. Here we demonstrate that an array of dipole lenses in alternate gradient configuration can be used to maintain transverse stability. A pulsed beam of metastable CO in high-field seeking states is accelerated from 275 to 289 m/s as well as decelerated from 275 to 260 m/s.     

Phoretic self-assembly of active colloidal molecules

We simulate the self-assembly of active colloidal molecules from binary mixtures of spherical particles using a Brownian dynamics algorithm. These particles interact via phoretic interactions, which are determined by two independently tunable parameters, surface activity and surface mobility. In systems composed of equal-size particles, we observe the formation of colloidal molecules with well-defined coordination numbers and spatial arrangement, which also display distinct dynamic functions, such as resting, translating, and rotating. By changing the size ratio to 2 : 1 between the two species,we further observe the formation of colloidal molecules with new structures arising from breaking the size symmetry. By tuning the mutual interactions between the smaller species via their surface mobility, we are able to control their spacing as well as the coordination number of the colloidal molecules. This study highlights the importance of tuning surface parameters and size asymmetry in controlling the structure and the active dynamics of colloidal molecules.     

单层石墨烯水分子吸附对其光学性质的影响

用基于第一性原理中的密度泛函理论MS软件对水分子吸附在单层石墨烯表面进行计算,使用广义梯度近似和周期性平面模型,得到不同数量的水分子吸附在石墨烯表面上的吸附能,并且计算了相对应的光学性质.得到的结果是吸附能很小,主要是范德瓦尔斯相互作用.石墨烯具有高疏水性,水分子在石墨烯表面对石墨烯的电子结构几乎没有作用,吸附不同个数的水分子后对石墨烯的光学性质有一定影响,其中吸附单个水分子后变化并不明显,吸附2或3个水分子后吸收率和光电导率略有下降;折射率和消光率下降不明显,说明吸附水对石墨烯的透明度影响不大;介电函数的实数部分变化趋于平缓,虚数部分有明显下降;能量损失增加.     

单层石墨烯水分子吸附对其光学性质的影响

用MS软件对水分子吸附在单层石墨烯表面进行计算,采用第一性原理中的密度泛函理论。使用广义梯度近似和周期性平面模型,得到不同数量的水分子吸附在石墨烯表面上的吸附能,并且计算了相对应的光学性质。得到的结果是吸附能很小,主要是范德瓦尔斯相互作用。石墨烯具有高疏水性,水分子在石墨烯表面对石墨烯的电子结构几乎没有作用,吸附不同个数的水分子后对石墨烯的光学性质有一定影响,其中吸附单个水分子后变化并不明显,吸附2或3个水分子后吸收率和光电导率略有下降;折射率和消光率下降不明显,说明吸附水对石墨烯的透明度影响不大;介电函数的实数部分变化趋于平缓,虚数部分有明显下降;能量损失增加。     

Study of dissipative tunneling controllability in systems of interacting quantum molecules

Controlled 2D dissipative tunneling in systems of coupled quantum molecules is studied in the quasi-classical (instanton) approximation. It is shown that, with allowance for the electron tunneling trajectory bifurcation, the effect of two-particle wave function blocking in a system of coupled quantum molecules is observed when the radii of quantum dots (making up the quantum molecules) coincide. If the influence of a thermostat medium is neglected, blocking is replaced by a “kink” in the tunneling probability as a function of the asymmetry parameter of quantum molecules.     

量子相干控制化学反应的进展和机遇

1995年 ,人们曾预言“量子控制多体动力学将成为化学物理的主流”(引自第 2 0届Ｓｏｌｖａｙ化学会议上ＳｔｕａｒｔＡ .Ｒｉｃｅ的主旨演说 .Ｓｏｌｖａｙ会议是研讨未来科学的高级会议 .这一届会议的主题是“光化学 :化学反应及其飞秒尺度上的控制”) .现在 ,我们看到了这股潮流正源源而来 ,每年都不断地在Ｎａｔｕｒｅ、Ｓｃｉｅｎｃｅ等杂志上刻下了里程碑 .人们一直希望控制化学反应的方向和历程 .早期的控制是被动的控制 ,即通过把握反应的宏观条件 (如温度、压力等 )或者选择适当的催化剂去实现 .自从分子反应动力学发展之后 ,人们在…     

Effect of dipole forces on the structure of the liquid phases of DNA

The dipole-dipole contribution to the energy of the pair interaction between DNA molecules has been calculated and analyzed. Rigid fragments of DNA, i.e., of a length of about the persistent length, which have discrete dipole moments of base pairs, are considered. For a given distance between the centers of mass of molecules, the energy of the dipole-dipole interaction is a function of three angular variables; the angles ?₁ and ?₂ between the central dipoles of both molecules and the z axis passing through the centers of the molecules, as well as the angle ξ between long axes of the molecules, are taken as these variables. It is shown that the dipole energy has minima when the mutual orientation of the molecules satisfies one of the following conditions: (i) ?₁ = ?₂ = 0 or (ii) ?₁ = ?₂ = π. The cholesteric twist angle ξ can be both positive and negative in dependence on the type of the minimum. For realistic cholesteric dispersion parameters, the dipole energy is only slightly lower than the experimentally known binding energy of the molecules in dispersion. The results allow the assumption that the dipole forces significantly affect the structure and other properties of DNA suspensions; in particular, they can lead to nontrivial texture phenomena, biaxial correlation, and multistability.     

Sputtering of molecules during low-energy electron bombardment of alkali halides

The emission of molecules during bombardment of several alkali halides with a 540 eV electron beam has been investigated. Using a time of flight method the energy distributions of the halogen molecules have been measured at various temperatures of the target. The relative halogen molecule to atom ratio has also been examined as a function of the target temperature. It has been found that the molecules were formed from the atoms at the alkali halide surface. This process and the subsequent desorption of the molecules account for the experimental results.