Communication: Determination of the bond dissociation energy (D0) of the water dimer,(H2O) 2, by velocity map imaging (original) (raw)
Related papers
J. Am. Chem. Soc. , 2012
The hydrogen bonding in water is dominated by pairwise dimer interactions, and the predissociation of the water dimer following vibrational excitation is reported here. Velocity map imaging was used for an experimental determination of the dissociation energy (D 0 ) of (D 2 O) 2 . The value obtained, 1244 ± 10 cm −1 (14.88 ± 0.12 kJ/mol), is in excellent agreement with the calculated value of 1244 ± 5 cm −1 (14.88 ± 0.06 kJ/mol). This agreement between theory and experiment is as good as the one obtained recently for (H 2 O) 2 . In addition, pair-correlated water fragment rovibrational state distributions following vibrational predissociation of (H 2 O) 2 and (D 2 O) 2 were obtained upon excitation of the hydrogen-bonded OH and OD stretch fundamentals, respectively. Quasi-classical trajectory calculations, using an accurate full-dimensional potential energy surface, are in accord with and help to elucidate experiment. Experiment and theory find predominant excitation of the fragment bending mode upon hydrogen bond breaking. A minor channel is also observed in which both fragments are in the ground vibrational state and are highly rotationally excited. The theoretical calculations reveal equal probability of bending excitation in the donor and acceptor subunits, which is a result of interchange of donor and acceptor roles. The rotational distributions associated with the major channel, in which one water fragment has one quantum of bend, and the minor channel with both water fragments in the ground vibrational state are calculated and are in agreement with experiment.
The Journal of Physical …, 2010
The state-to-state vibrational predissociation dynamics of the hydrogen-bonded HCl-H 2 O dimer were studied following excitation of the HCl stretch of the dimer. Velocity-map imaging and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the HCl stretch of the dimer, HCl fragments were detected by 2 + 1 REMPI via the f 3 ∆ 2 r X 1 Σ + and V 1 Σ + r X 1 Σ + transitions. REMPI spectra clearly show HCl from dissociation produced in the ground vibrational state with J′′ up to 11. The fragments' center-of-mass translational energy distributions were determined from images of selected rotational states of HCl and were converted to rotational state distributions of the water cofragment. All the distributions could be fit well when using a dimer dissociation energy of D 0 ) 1334 ( 10 cm -1 . The rotational distributions in the water cofragment pair-correlated with specific rotational states of HCl appear nonstatistical when compared to predictions of the statistical phase space theory. A detailed analysis of pair-correlated state distributions was complicated by the large number of water rotational states available, but the data show that the water rotational populations increase with decreasing translational energy. † Part of the "Reinhard Schinke Festschrift".
Imaging H2O Photofragments in the Predissociation of the HCl− H2O Hydrogen-Bonded Dimer
Journal of Physical …, 2011
The state-to-state vibrational predissociation (VP) dynamics of the hydrogenbonded HCl-H 2 O dimer was studied following excitation of the dimer's HCl stretch by detecting the H 2 O fragment. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the HCl stretch of the dimer, H 2 O fragments were detected by 2 þ 1 REMPI via the C 1 B 1 (000) r X 1 A 1 (000) transition. REMPI spectra clearly show H 2 O from dissociation produced in the ground vibrational state. The fragments' center-of-mass (c.m.) translational energy distributions were determined from images of selected rotational states of H 2 O and were converted to rotational state distributions of the HCl cofragment. The distributions were consistent with the previously measured dissociation energy of D 0 = 1334 ( 10 cm -1 and show a clear preference for rotational levels in the HCl fragment that minimize translational energy release. The usefulness of 2 þ 1 REMPI detection of water fragments is discussed.
J. Phys. Chem. A, 2013
We report a joint experimental-theoretical study of the predissociation dynamics of the water trimer following excitation of the hydrogen bonded OH-stretch fundamental. The bond dissociation energy (D 0 ) for the (H 2 O) 3 → H 2 O + (H 2 O) 2 dissociation channel is determined from fitting the speed distributions of selected rovibrational states of the water monomer fragment using velocity map imaging. The experimental value, D 0 = 2650 ± 150 cm −1 , is in good agreement with the previously determined theoretical value, 2726 ± 30 cm −1 , obtained using an ab initio full-dimensional potential energy surface (PES) together with Diffusion Monte Carlo calculations [Wang; Bowman. J. Chem. Phys. 2011, 135, 131101]. Comparing this value to D 0 of the dimer places the contribution of nonpairwise additivity to the hydrogen bonding at 450−500 cm −1 . Quasiclassical trajectory (QCT) calculations using this PES help elucidate the reaction mechanism. The trajectories show that most often one hydrogen bond breaks first, followed by breaking and re-forming of hydrogen bonds (often with different hydrogen bonds breaking) until, after many picoseconds, a water monomer is finally released. The translational energy distributions calculated by QCT for selected rotational levels of the monomer fragment agree with the experimental observations. The product translational and rotational energy distributions calculated by QCT also agree with statistical predictions. The availability of low-lying intermolecular vibrational levels in the dimer fragment is likely to facilitate energy transfer before dissociation occurs, leading to statistical-like product state distributions.
Imaging bond breaking and vibrational energy transfer in small water containing clusters
CPL Frontiers, 2013
This letter presents a brief overview of our recent experimental studies of state-to-state vibrational predissociation (VP) dynamics of small hydrogen bonded (H-bonded) clusters following vibrational excitation. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) are used to determine accurate bond dissociation energies (D 0 ) of (H 2 O) 2 , (H 2 O) 3, HCl-H 2 O and NH 3 -H 2 O. Pair-correlated product energy distributions from the VP of these complexes are also presented and compared to theoretical models. Further insights into mechanisms are obtained from the recent quasi-classical trajectory (QCT) calculations of Bowman and coworkers. The D 0 values for (H 2 O) 2 and (H 2 O) 3 are in very good agreement with recent calculated values, and the results are used to estimate the contributions of cooperative interactions to the H-bonding network.
Imaging the State-Specific Vibrational Predissociation of the Ammonia-Water Hydrogen-Bonded Dimer
The journal of physical …, 2009
The state-to-state vibrational predissociation (VP) dynamics of the hydrogen-bonded ammonia-water dimer were studied following excitation of the bound OH stretch. Velocity-map imaging (VMI) and resonanceenhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the bound OH stretch fundamental, ammonia fragments were detected by 2 + 1 REMPI via the B 1 E′′ r X 1 A 1 ′ transition. The REMPI spectra show that NH 3 is produced with one and two quanta of the symmetric bend (ν 2 umbrella mode) excitation, as well as in the ground vibrational state. Each band is quite congested, indicating population in a large number of rotational states. The fragments' center-of-mass (c.m.) translational energy distributions were determined from images of selected rotational levels of ammonia with zero, one, or two quanta in ν 2 and were converted to rotational state distributions of the water cofragment. All the distributions could be fit well by using a dimer dissociation energy of D 0 ) 1538 ( 10 cm -1 . The rotational state distributions in the water cofragment pair-correlated with specific rovibrational states of ammonia are broad and include all the J KaKc states allowed by energy conservation. The rotational populations increase with decreasing c.m. translational energy. There is no evidence for ammonia products with significant excitation of the asymmetric bend (ν 4 ) or water products with bend (ν 2 ) excitation. The results show that only restricted pathways lead to predissociation, and these do not always give rise to the smallest possible translational energy release, as favored by momentum gap models. Figure 1. Equilibrium geometry of the ammonia-water dimer (ref. 32). R(N-O) ) 2.989 Å; θ N ) 23.1°; θ O ) 49.
Chemical Physics Letters, 2013
Triple-resonance vibrational spectroscopy is used to determine the lowest dissociation energy, D 0 , for the water isotopologue HD 16 O as 41 239.7 ±0.2 cm −1 and to improve D 0 for H 2 16 O to 41 145.92 ±0.12 cm −1 . Ab initio calculations including systematic basis set and electron correlation convergence studies, relativistic and Lamb shift effects as well as corrections beyond the Born-Oppenheimer approximation, agree with the measured values to 1 and 2 cm −1 respectively. The improved treatment of high-order correlation terms is key to this high theoretical accuracy. Predicted values for D 0 for the other five major water isotopologues are expected to be correct within 1 cm −1 .
Water dimer hydrogen bond stretch, donor torsion overtone, and “in-plane bend” vibrations
The Journal of Chemical Physics, 2003
We report the measurement and analysis of 64 new K a ϭ0←0,1 and K a ϭ1←0,1 transitions of (H 2 O) 2 and 16 new K a ϭ0←0 transitions of (D 2 O) 2 by terahertz laser vibration-rotationtunneling spectroscopy of a planar supersonic expansion between 140.5 and 145.5 cm Ϫ1 . The transitions in both isotopomers correspond to AЈ vibrations assigned to the hydrogen bond stretch ͑translational͒ and donor torsion overtone vibrations. The interchange splitting is 56.3 GHz in K a ϭ0 of the excited state of (H 2 O) 2 , nearly 3 times the value of the ground state, and the bifurcation tunneling splitting is 1.8 GHz, over 2 times the value of the ground state. We compare the existing experimental spectra with calculations on state-of-the-art intermolecular potential energy surfaces and critically review the vibrational assignments reported in the literature. We show that the discrepancy between theory and experiment regarding the assignment of the feature near 103 cm Ϫ1 can be resolved by considering E 2 →E 1 transitions, which had not been considered previously.
Rapid bond rearrangement in core-excited molecular water
Physical Chemistry Chemical Physics, 2013
The angular anisotropy of fragments created in the dissociation of core-electron excited water molecules is studied to probe the correlation between fragmentation channels, kinematics and molecular geometry. We present fragment kinetic measurements for water molecules where the innershell oxygen electron is excited to the unoccupied 4a 1 and 2b 2 valence molecular orbitals. The kinematics of individual fragmentation channels are measured using fully three-dimensional momentum imaging of fragments. The results show that the geometry of the molecule and the kinetic energy of fragments are strongly coupled in the atomisation process. In addition we identify a fragmentation process arising from bond rearrangement evidenced by the H 2 + -O + ion pair which is accessible for resonant excitation of the 1s electron. In all of the two-body fragmentation processes the dissociation takes place along the potential-energy surface, while atomisation reveals both dissociation along the potential surface and Coulomb explosion. The angular distribution of fragments suggests that the bond rearrangement is very rapid; likely on a sub 10 fs time scale.
Vibrational predissociation of the phenol–water dimer: a view from the water
Physical Chemistry Chemical Physics, 2019
The vibrational predissociation (VP) dynamics of the phenol-water (PhOH-H 2 O) dimer were studied by detecting H 2 O fragments and using velocity map imaging (VMI) to infer the internal energy distributions of PhOH cofragments, pair-correlated with selected rotational levels of the H 2 O fragments. Following infrared (IR) laser excitation of the hydrogen-bonded OH stretch fundamental of PhOH (Pathway 1) or the asymmetric OH stretch localized on H 2 O (Pathway 2), dissociation to H 2 O + PhOH was observed. H 2 O fragments were monitored state-selectively by using 2+1 Resonance-Enhanced Multiphoton Ionization (REMPI) combined with time-of-flight mass spectrometry (TOF-MS). VMI of H 2 O in selected rotational levels was used to derive center-of-mass (c.m.) translational energy (E T) distributions. The pair-correlated internal energy distributions of the PhOH cofragments derived via Pathway 1 were well described by a statistical prior distribution. On the other hand, the corresponding distributions obtained via Pathway 2 show a propensity to populate higher-energy rovibrational levels of PhOH than expected from a statistical distribution and agree better with an energy-gap model. The REMPI spectra of the H 2 O fragments from both pathways could be fit by Boltzmann plots truncated at the maximum allowed energy, with a higher temperature for Pathway 2 than that for Pathway 1. We conclude that the VP dynamics depends on the OH stretch level initially excited.