Rates of conversions of molecular internal energy to and from kinetic energy by means of molecular collision allows to compute collisional line shapes and transport properties of gases. Knowledge of ro-vibrational quenching rates is necessary to connect spectral observations to physical properties of warm astrophysical gasses, including exo-atmospheres. For a system of paramount importance in this context, the vibrational bending mode quenching of H2O by H2, we show here that exchange of vibrational to rotational and kinetic energy remains a quantum process, despite the large numbers of quantum levels involved and the large vibrational energy transfer. The excitation of the quantized rotor of the projectile is by far the most effective ro-vibrational quenching path of water. To do so, we use a fully quantum first principle computation, potential and dynamics, converging it at all stages, in a full coupled channel formalisms. We present here rates for the quenching of the first bendingmode of ortho-H2O by ortho H2, up to 500K, in a fully converged coupled channels formalism.
We present a study of vibrational quenching and chemical processes of molecular ions immersed in an ultracold atomic gas by means of the quasi-classical trajectory (QCT) method. In particular, BaRb$^+(v)$ + Rb collisions are studied at cold temperatures revealing a highly efficient energy transfer between the translational degrees of freedom and internal degrees of the molecular ion. Thus leading to a large vibrational quenching cross section which follows the Langevin capture model prediction. These results play a key role on the understanding of relaxation phenomena of cold molecular ions in…
The vibrational quenching cross sections and corresponding low-temperature rate constants for the v = 1 and v = 2 states of CN- colliding with He and Ar atoms have been computed ab initio using new three dimensional potential energy surfaces. Little work has so far been carried out on low-energy vibrationally inelastic collisions for anions with neutral atoms. The cross sections and rates calculated at energies and temperatures relevant for both ion traps and astrochemical modelling, are found by the present calculations to be even smaller than those of the similar C2- /He and C2-/Ar systems w…
The dicarbon molecular anion is currently of interest as a candidate for laser cooling due to its electronic structure and favorable branching ratios to the ground electronic and vibrational states. Helium has been proposed as a buffer gas to cool the molecule's internal motion. We calculate the cross sections and corresponding rates for rovibrational inelastic collisions of the dicarbon anion with He, and also with Ne and Ar, on three-dimensional ab initio potential energy surfaces using quantum scattering theory. The rates for vibrational quenching with He and Ne are very small and are simil…
Interstellar and cometary ices play an important role in the formation of planetary systems around young stars. Their main constituent is amorphous solid water (ASW). Although ASW is widely studied, vibrational energy dissipation and structural changes due to vibrational excitation are less well understood. The hydrogen-bonding network is likely a crucial component in this. Here we present experimental results on hydrogen-bonding changes in ASW induced by the intense, nearly monochromatic mid-IR free-electron laser (FEL) radiation of the FELIX-2 beamline at the HFML-FELIX facility at the Radbo…
The hydrogen bond is usually described within the clamped nucleus approximation in which electronic and vibrational motions are considered separately. This approach leads to a double-well potential which facilitates proton tunnelling. In this work, the hydrogen bond is described by a formalism based on the non-adiabatic Hamiltonian in which electronic and vibrational motions are coupled. Quasi-degeneracy associated with the hydrogen bond supports this approach which is shown to afford an alternative picture of proton tunnelling.
The properties of the hydrogen bonds in ethylammonium nitrate are analyzed by using molecular dynamics simulations and infrared as well as nuclear magnetic resonance experiments. Ethylammonium nitrate features a flexible three-dimensional network of hydrogen bonds with moderate strengths, which makes it distinct from related triethylammonium-based ionic liquids. First, the network's flexibility is manifested in a not very pronounced correlation of the hydrogen bond geometries, which is caused by rapid interchanges of bonding partners. The large flexibility of the network leads to a substantial…
The relative orientation of colliding molecules plays a key role in determining the rates of chemical processes. Here we examine in detail a prototypical example: rotational quenching of HD in cold collisions with H2. We show that the rotational quenching rate from j=2 -> 0, in the v=1 vibrational level, can be maximized by aligning the HD along the collision axis and can be minimized by aligning the HD at the so called magic angle. This follows from quite general helicity considerations and suggests that quenching rates for other similar systems can also be controlled in this manner.
In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and non-confinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave f…
Schrödinger equation with Pauli-Fierz Hamiltonian and double well potential as model of vibrationally enhanced tunneling for proton transfer in hydrogen bond
Extended study of crystal structures, optical properties and vibrational spectra of polar 2-aminopyrimidinium hydrogen phosphite and bis(2-aminopyrimidinium) sulfate monohydrate and two 2-aminopyrimidinium hydrogen sulfate polymorphs
Representation of molecular vibrational degrees of freedom by independent harmonic oscillators, when describing electronic spectra or electronic excitation energy transport, raises unfavourable effects as vibrational energy relaxation becomes inaccessible. A standard theoretical description is extended in this paper by including both electronic-phonon and vibrational-phonon couplings. Using this approach we have simulated a model pigment-protein system and have shown that intermode coupling leads to the quenching of pigment vibrational modes, and to the redistribution of fluctuation spectral d…
Theoretical analysis of the effect of an external vibration on proton transfer (PT) in a hydrogen bond (HB) is carried out. It is based on the two-dimensional Schrödinger equation with trigonometric double-well potential. Its solution obtained within the framework of the standard adiabatic approximation is available. An analytic formula is derived that provides the calculation of PT rate with the help of elements implemented in {\sl {Mathematica}}. We exemplify the general theory by calculating PT rate constant for the intermolecular HB in the Zundel ion ${\rm{H_5O_2^{+}}}$ (oxonium hydrate). …
High-resolution coherent Raman spectroscopic measurements of all three tritium-containing molecular hydrogen isotopologues T$_2$, DT and HT were performed to determine the ground electronic state fundamental Q-branch ($v=0 \rightarrow 1, ΔJ = 0$) transition frequencies at accuracies of $0.0005$ cm$^{-1}$. An over hundred-fold improvement in accuracy over previous experiments allows the comparison with the latest ab initio calculations in the framework of Non-Adiabatic Perturbation Theory including nonrelativisitic, relativisitic and QED contributions. Excellent agreement is found between exper…
Accurate rate coefficients for molecular vibrational transitions due to collisions with H$_2$, critical for interpreting infrared astronomical observations, are lacking for most molecules. Quantum calculations are the primary source of such data, but reliable values that consider all internal degrees of freedom of the collision complex have only been reported for H$_2$-H$_2$ due to the difficulty of the computations. Here we present essentially exact full-dimensional dynamics computations for rovibrational quenching of CO due to H$_2$ impact. Using a high-level six-dimensional potential surfac…
Quantum reactive scattering calculations on the vibrational quenching of HD due to collisions with H were carried out employing an accurate potential energy surface. The state-to-state cross sections for the chemical reaction HD ($v=1, \ j=0$) + H $\rightarrow$ D + H$_2$ ($v'=0, \ j'$) at collision energies between 1 and 10,000 cm$^{-1}$ are presented, and a Feshbach resonance in the low-energy regime, below the reaction barrier, is observed for the first time. The resonance is attributed to coupling with the vibrationally adiabatic potential correlating to the $v=1, \ j=1$ level of the HD mol…
Amorphous solid water (ASW) is abundantly present in the interstellar medium, where it forms a mantle on interstellar dust particles and it is the precursor for cometary ices. In space, ASW acts as substrate for interstellar surface chemistry leading to complex molecules and it is postulated to play a critical role in proton-transfer reactions. Although ASW is widely studied and is generally well characterized by different techniques, energetically-induced structural changes, such as ion, electron and photon irradiation, in these materials are less well understood. Selective pumping of specifi…
The simplest molecules in nature, molecular hydrogen ions in the form of H2+ and HD+, provide an important benchmark system for tests of quantum electrodynamics in complex forms of matter. Here, we report on such a test based on a frequency measurement of a vibrational overtone transition in HD+ by laser spectroscopy. We find that the theoretical and experimental frequencies are equal to within 0.6(1.1) parts per billion, which represents the most stringent test of molecular theory so far. Our measurement not only confirms the validity of high-order quantum electrodynamics in molecules, but al…
The mass-correction function is evaluated for selected excited states of the hydrogen molecule within a single-state non-adiabatic treatment. Its qualitative features are studied under the avoided crossing of the $EF$ with the $GK$ state and also for the outer well of the $H\bar{H}$ state. For the $H\bar{H}$ state, a negative mass correction is obtained for the vibrational motion near the outer minimum, which accounts for most of the deviation between experiment and earlier theoretical work.
First-principles approach to rotational-vibrational frequencies and infrared intensity for H$_2$ adsorbed in nanoporous materials
利用van der Waals密度泛函理论计算了H $_2$在金属-有机骨架中的吸附位和低转动振动能级.由于键拉伸的诱导偶极子被发现准确地给出了第一性原理驱动的近似使用最大本地化的Wannier函数分析。RV跃迁的复杂光谱中的谱线的强度和位置与实验合理地一致，特别是解释了实验中神秘地丢失的仲氢的主要谱线。
Hydrogen bonds are of paramount importance in the chemistry of clays, mediating the interaction between the clay surface and water, and for some materials between separate layers. It is well-established that the accuracy of a computational model for clays depends on the level of theory at which the electronic structure is treated. However, for hydrogen-bonded systems the motion of light H nuclei on the electronic potential energy surface is often affected by quantum delocalization. Using path integral molecular dynamics, we show that nuclear quantum effects lead to a relatively small change in…
HF trimer: 12D fully coupled quantum calculations of HF-stretch excited intramolecular and intermolecular vibrational states using contracted bases of intramolecular and intermolecular eigenstates
Infrared pump-probe spectroscopy provides detailed information on the dynamics of hydrogen-bonded liquids. Due to dissipation of the absorbed pump pulse energy, also thermal equilibration dynamics contributes to the observed signal. Disentangling this contribution from the molecular response remains an open challenge. Performing non-equilibrium molecular dynamics simulat ions of liquid deuterated methanol, we show that faster molecular vibrational relaxation and slower heat diffusion are decoupled and occur on different length scale. Transient structures of the hydrogen bonding network influen…
We present numerical results for rate coefficients of reaction and vibrational quenching in the collision of H with D$_2(v,j)$ at cold and ultracold temperatures. We explore both ortho-D$_2(j\!=\!0)$ and para-D$_2(j\!=\!1)$ for several initial vibrational states $(v\leq 5)$, and find resonant structures in the energy range 0.01--10 kelvin, which are sensitive to the initial rovibrational state $(v,j)$. We compare the reaction rates for D$_2$+H with our previously obtained results for the isotopologue reaction H$_2$+D, and discuss the implications of our detailed study of this benchmark system …
We develop a formalism to directly evaluate the matrix of force constants within a Quantum Monte Carlo calculation. We utilize the matrix of force constants to accurately relax the positions of atoms in molecules and determine their vibrational modes, using a combination of Variational and Diffusion Monte Carlo. The computed bond lengths differ by less than 0.007Å from the experimental results for all four tested molecules. For hydrogen and hydrogen chloride, we obtain fundamental vibrational frequencies within 0.1% of experimental results and ~10 times more accurate than leading computational…
The hydrogen phase diagram has a number of unusual features which are generally well reproduced by density functional calculations. Unfortunately, these calculations fail to provide good physical insights into why those features occur. In this paper, we parameterize a model potential for molecular hydrogen which permits long and large simulations. The model shows excellent reproduction of the phase diagram, including the broken-symmetry Phase II, an efficiently-packed phase III and the maximum in the melt curve. It also gives an excellent reproduction of the vibrational frequencies, including …
Hydrogen bonding in water under extreme confinement
Stanford University（斯坦福大学）；Massachusetts Institute of Technology（麻省理工学院）；Brown University（布朗大学）；Vanderbilt University（范德堡大学）；University of Washington（华盛顿大学）；Pacific Northwest National Laboratory（太平洋西北国家实验室）；Oak Ridge National Laboratory（橡树岭国家实验室）；SLAC National Laboratory（斯坦福直线加速器中心国家实验室）
Accurate $EF{}^1Σ^+_g-X{}^1Σ^+_g$ transition energies in molecular hydrogen were determined for transitions originating from levels with highly-excited vibrational quantum number, $v=11$, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited H$_2^*$, produced via the photodissociation of H$_2$S, yielding transition frequencies with accuracies of $45$ MHz or $0.0015$ cm$^{-1}$. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing $7pπ$ electronic Rydberg states, resulting in narrow transitions du…
