First-principles rotation–vibration spectrum of water above dissociation (original) (raw)
Related papers
State-selective spectroscopy of water up to its first dissociation limit
The Journal of Chemical Physics, 2009
A joint experimental and first-principles quantum chemical study of the vibration-rotation states of the water molecule up to its first dissociation limit is presented. Triple-resonance, quantum state-selective spectroscopy is used to probe the entire ladder of water's stretching vibrations up to 19 quanta of OH stretch, the last stretching state below dissociation. A new ground state potential energy surface of water is calculated using a large basis set and an all-electron, multireference configuration interaction procedure, which is augmented by relativistic corrections and fitted to a flexible functional form appropriate for a dissociating system. Variational nuclear motion calculations on this surface are used to give vibrational assignments. A total of 44 new vibrational states and 366 rotation-vibration energy levels are characterized; these span the region from 35 508 to 41 126 cm −1 above the vibrational ground state.
State-resolved spectroscopy of high vibrational levels of water up to the dissociative continuum
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012
We summarize here our experimental studies of the high rovibrational energy levels of water. The use of double-resonance vibrational overtone excitation followed by energy-selective photofragmentation and laser-induced fluorescence detection of OH fragments allowed us to measure previously inaccessible rovibrational energies above the seventh OH-stretch overtone. Extension of the experimental approach to triple-resonance excitation provides access to rovibrational levels via transitions with significant transition dipole moments (mainly OH-stretch overtones) up to the dissociation threshold of the O–H bond. A collisionally assisted excitation scheme enables us to probe vibrations that are not readily accessible via pure laser excitation. Observation of the continuous absorption onset yields a precise value for the O–H bond dissociation threshold, 41 145.94 ± 0.15 cm −1 . Finally, we detect long-lived resonances as sharp peaks in spectra above the dissociation threshold.
Journal of Quantitative Spectroscopy and Radiative Transfer, 2010
A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron massvelocity and Darwin corrections. For H 2 16 O, the PES has a dissociation energy of D 0 = 41 109 cm À 1 and supports 1150 vibrational energy levels up to 41 083 cm À 1 . The deviation between the computed and the experimentally measured energy levels is below 15 cm À 1 for all the states with energies less than 39 000 cm À 1 . Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26 500 cm À 1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed.
Calculation of the rotation–vibration states of water up to dissociation
The Journal of Chemical Physics, 1998
We present rotation-vibrational levels of water up to the dissociation limit using two recent, global potential energy surfaces. These calculations are performed using our recently developed discrete variable representation ͑DVR͒ based parallel code ͑PDVR3D͒, which runs on computers with massively parallel processors. Variational tests on the convergence of these results show convergence within 0.5 cm Ϫ1 . Analysis of the highest wave functions for the vibrational energy levels are also shown. Tests on previous calculations performed using conventional computers suggest that convergence for high-lying rotationally excited states is not as good as claimed.
2013
A recently computed, high-accuracy ab initio Born−Oppenheimer (BO) potential energy surface (PES) for the water molecule is combined with relativistic, adiabatic, quantum electrodynamics, and, crucially, nonadiabatic corrections. Calculations of ro-vibrational levels are presented for several water isotopologues and shown to have unprecedented accuracy. A purely ab initio calculation reproduces some 200 known band origins associated with seven isotopologues of water with a standard deviation (σ) of about 0.35 cm −1. Introducing three semiempirical scaling parameters, two affecting the BO PES and one controlling nonadiabatic effects, reduces σ below 0.1 cm −1. Introducing one further rotational nonadiabatic parameter gives σ better than 0.1 cm −1 for all observed rovibrational energy levels up to J = 25. We conjecture that the energy levels of closed-shell molecules with roughly the same number of electrons as water, such as NH 3 , CH 4 , and H 3 O + , could be calculated to this accuracy using an analogous procedure. This means that near-ab initio calculations are capable of predicting transition frequencies with an accuracy only about a factor of 5 worse than high resolution experiments.
J Phys Chem a, 2000
The aim of the present paper is to evaluate the influence of the solute-solvent interactions on the infrared spectra of water diluted in liquid CCl 4 and in supercritical xenon, considered as the standard 'inert' solvent. This investigation is based upon FTIR spectra analyzed at the light of both analytical treatments and molecular dynamics simulations. For water in supercritical xenon, the rotational relaxation processes mainly determine the shape of the IR profiles associated with the ν 1 and ν 3 stretching modes. The water molecule rotates almost "freely" due to the isotropic character of the van der Waals interactions applied on the solute. Both the J-model for asymmetric molecular rotor and the molecular dynamics simulations properly account for the band shapes associated with the ν 3 and ν 1 vibrational modes of water. Thus, the rotational dynamics of water is primarily governed by "collisional" interactions with the neighboring solvent molecules. For water dissolved in liquid CCl 4 , a structural analysis based upon the simulated radial distribution functions provides evidence for the existence of a short-ranged C‚‚‚H-O arrangement between the solute and its neighboring solvent molecules. It is also found that the reorientational dynamics of water are more perturbed than those in SC xenon fluid, due to the weakly anisotropic character of the water-CCl 4 interactions. In particular, the reorientational motions of the z symmetry axis of water appear to be more specifically affected. We emphasize that a correct treatment of the rotational dynamics of water in liquid CCl 4 is provided only by simulation methods that, in contrast to the analytical J model, include the details of the intermolecular solute-solvent potential. Although the transition dipole moment of the ν 3 mode of water is only weakly affected by the interactions, the oscillator strength of the ν 1 internal mode is found to be enhanced compared to its gas-phase value, a result related to the increase of the transition dipole moment due to the water-solvent interactions. Finally, we argue that the spectral properties can be interpreted without invoking a specific H-bond contribution in the intermolecular potential.
Vibration-rotation levels of water beyond the Born-Oppenheimer approximation
Chemical Physics Letters, 1996
The value of the adiabatic correction to the Born-Oppenheimer electronic energy is calculated as a function of geometry for water using SCF wavefunctions. A mass-dependent adiabatic function is combined with high-accuracy ab initio electronic structure calculations due to Partridge and Schwenke. Vibrational band origins for H20, D20, T20, HDO, HTO and DTO are analysed. Unlike previous calculations on the H + system, it is suggested that non-adiabatic effects are more important 3 than adiabatic ones in determining accurate isotope dependence of the vibrational band origins of water. Use of the adiabatic surface and effective masses of the heavy particles intermediate between the nuclear and atomic masses is found to significantly improve predictions of rotational term values. The adiabatic correction is found to be of particular importance for rotational levels with high K,,.
The Journal of Chemical Physics, 2007
Quantum dynamical calculations are reported for the zero point energy, several low-lying vibrational states, and the infrared spectrum of the H 5 O 2 + cation. The calculations are performed by the multiconfiguration time-dependent Hartree ͑MCTDH͒ method. A new vector parametrization based on a mixed Jacobi-valence description of the system is presented. With this parametrization the potential energy surface coupling is reduced with respect to a full Jacobi description, providing a better convergence of the n-mode representation of the potential. However, new coupling terms appear in the kinetic energy operator. These terms are derived and discussed. A mode-combination scheme based on six combined coordinates is used, and the representation of the 15-dimensional potential in terms of a six-combined mode cluster expansion including up to some 7-dimensional grids is discussed. A statistical analysis of the accuracy of the n-mode representation of the potential at all orders is performed. Benchmark, fully converged results are reported for the zero point energy, which lie within the statistical uncertainty of the reference diffusion Monte Carlo result for this system. Some low-lying vibrationally excited eigenstates are computed by block improved relaxation, illustrating the applicability of the approach to large systems. Benchmark calculations of the linear infrared spectrum are provided, and convergence with increasing size of the time-dependent basis and as a function of the order of the n-mode representation is studied. The calculations presented here make use of recent developments in the parallel version of the MCTDH code, which are briefly discussed. We also show that the infrared spectrum can be computed, to a very good approximation, within D 2d symmetry, instead of the G 16 symmetry used before, in which the complete rotation of one water molecule with respect to the other is allowed, thus simplifying the dynamical problem.
Molecular Physics, 2006
Carr-Parrinello MD calculations for a simplistic periodic model of liquid water are performed to probe temperature dependence of infrared activation lifetime. IR activation is classically simulated by adding an appropriate velocity to the proton in a tagged water molecule. The evolution of hydrogen bonding descriptors is monitored through consecutive simulations to spot the onset of qualitative changes in the hydrogen bonding network; they are related to vibrational energy relaxation. The applied ionic simulation temperature (elevated by 20%) decreases the tendency to overbinding characteristic for CP MD calculations. Qualitatively estimated stretch lifetimes are 280, 320 and 400 fs for temperatures of 298, 320 and 370 K, respectively. This work gives direct evidence of the parallel dependence of both the decay of OH activation and the hydrogen bond network on temperature, which offers a viable explanation for the experimentally observable unusual increase in OH excitation lifetime with temperature.