Imaging the State-Specific Vibrational Predissociation of the Hydrogen Chloride− Water Hydrogen-Bonded Dimer† (original) (raw)
Related papers
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.
The Journal of chemical …, 2011
The bond dissociation energy (D 0 ) of the water dimer is determined by using state-to-state vibrational predissociation measurements following excitation of the bound OH stretch fundamental of the donor unit of the dimer. Velocity map imaging and resonance-enhanced multiphoton ionization (REMPI) are used to determine pair-correlated product velocity and translational energy distributions. H 2 O fragments are detected in the ground vibrational (000) and the first excited bending (010) states by 2 + 1 REMPI via theC 1 B 1 (000) ←X 1 A 1 (000 and 010) transitions. The fragments' velocity and center-of-mass translational energy distributions are determined from images of selected rovibrational levels of H 2 O. An accurate value for D 0 is obtained by fitting both the structure in the images and the maximum velocity of the fragments. This value, D 0 = 1105 ± 10 cm −1 (13.2 ± 0.12 kJ/mol), is in excellent agreement with the recent theoretical value of D 0 = 1103 ± 4 cm −1 (13.2 ± 0.05 kJ/mol) suggested as a benchmark by Shank et al.
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.
J. Phys. Chem. A, 2014
The breaking of hydrogen bonds in molecular 9 systems has profound effects on liquids, e.g., water, biomolecules 10 (e.g., DNA), etc., and so it is no exaggeration to assert the 11 importance of these bonds to living systems. However, despite 12 years of extensive research on hydrogen bonds, many of the 13 details of how these bonds break and the corresponding energy 14 redistribution processes remain poorly understood. Here we 15 report extensive experimental and theoretical insights into the 16 breakup of two or three hydrogen bonds of the dissociation of a 17 paradigm system of a hydrogen-bonded network, the ring HCl trimer. Experimental state-to-state vibrational predissociation 18 dynamics of the trimer following vibrational excitation were studied by using velocity map imaging and resonance-enhanced 19 multiphoton ionization, providing dissociation energies and product state distributions for the trimer's breakup into three 20 separate monomers or into dimer + monomer. Accompanying the experiments are high-level calculations using diffusion Monte 21 Carlo and quasiclassical simulations, whose results validate the experimental ones and further elucidate energy distributions in the 22 products. The calculations make use of a new, highly accurate potential energy surface. Simulations indicate that the dissociation 23 mechanism requires the excitation to first relax into low-frequency motions of the trimer, resulting in the breaking of a single 24 hydrogen bond. This allows the system to explore a critical van der Waals minimum region from which dissociation occurs 25 readily to monomer + dimer.
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.
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.
Energetics and Predissociation Dynamics of Small Water, HCl, and Mixed HCl−Water Clusters
This Review summarizes recent research on vibrational predissociation (VP) of hydrogen-bonded clusters. Specifically, the focus is on breaking of hydrogen bonds following excitation of an intramolecular vibration of the cluster. VP of the water dimer and trimer, HCl clusters, and mixed HCl−water clusters are the major topics, but related work on hydrogen halide dimers and trimers, ammonia clusters, and mixed dimers with polyatomic units are reviewed for completion and comparison. The theoretical focus is on generating accurate potential energy surfaces (PESs) that can be used in detailed dynamical calculations, mainly using the quasiclassical trajectory approach. These PESs have to extend from the region describing large amplitude motion around the minimum to regions where fragments are formed. The experimental methodology exploits velocity map imaging to generate pair-correlated product translational energy distributions from which accurate bond dissociation energies of dimers and trimers and energy disposal in fragments are obtained. The excellent agreement between theory and experiment on bond dissociation energies, energy disposal in fragments, and the contributions of cooperativity demonstrates that it is now possible, with state-of-the-art experimental and theoretical methods, to make accurate predictions about dynamical and energetic properties of dissociating clusters. CONTENTS
Chinese Journal of Chemical Physics, 2021
We report full-dimensional and fully coupled quantum bound-state calculations of the J=1 intra-and intermolecular rovibrational states of two isotopologues of the hydrogen chloride-water dimer, HCl-H 2 O (HH) and DCl-H 2 O (DH). The present study complements our recent theoretical investigations of the J=0 nine-dimensional (9D) vibrational level structure of these and two other H/D isotopologues of this noncovalently bound molecular complex, and employs the same accurate 9D permutation invariant polynomial-neural network potential energy surface. The calculations yield all intramolecular vibrational fundamentals of the HH and DH dimers and the low-energy intermolecular rovibrational states in these intramolecular vibrational manifolds. The results are compared with those of the 9D J=0 calculations of the same dimers. The energy differences between the K=1 and K=0 eigenstates exhibit pronounced variations with the intermolecular rovibrational states, for which a qualitative explanation is provided.
First-principles rotation–vibration spectrum of water above dissociation
Chemical Physics Letters, 2011
High-level ab initio electronic structure and variational nuclear motion computations are combined to simulate the spectrum of the water molecule at and above its first dissociation limit. Results of these computations are compared with the related state-selective multi-photon measurements of Grechko et al. [J. Chem. Phys. 138 ]. Both measured and computed spectra show pronounced structures due to quasi-bound (resonance) states. Traditional resonance features associated with trapping of vibrational or rotational energy of the system are identified and assigned. A strong and broad feature observed slightly above dissociation is found to be associated with direct photodissociation into the continuum.
Chemical Physics, 1995
The mechanism for the reaction of atomic chlorine with vibrationally excited methane is investigated by measurement of correlated state and scattering distributions using the method of core extraction (see preceding paper). Laser photolysis of molecular chlorine creates monoenergetic chlorine atoms (≳98% Cl 2P3/2) that react with vibrationally excited methane molecules prepared by linearly polarized infrared laser excitation. The resulting HCl product population distributions are determined by (2+1) resonance-enhanced multiphoton ionization (REMPI), and the differential cross section for each product rovibrational state is measured by core extraction. Approximately 30% of the product is formed in HCl(υ=1,J) with a cold rotational distribution; the remaining population is formed in HCl(υ=0,J) and is more rotationally excited. We observe a rich variation of the scattered flux that is dependent on the internal-energy state of the product. The HCl(υ=1) product is sharply forward scattered for low J and becomes nearly equally forward-backward scattered for high J; the HCl(υ=0,J) product is back and side scattered. The reactions of Cl with C-H stretch-excited methane (CH4) and C-H stretch-excited CHD3 are found to have similar angular and internal-state distributions. Observation of the spatial anisotropy of the HCl(υ=0, J=3) product shows that significant vibrational excitation of the methyl fragment does not occur. The measured spatial anisotropy is most consistent with a model in which backscattered HCl(υ=0, J=3) is formed in coincidence with slight methyl vibrational excitation and the forward-scattered HCl(υ=0, J=3) is formed in coincidence with no methyl excitation. The approach of the attacking chlorine atom with respect to the C-H stretch direction can be varied by rotating the plane of polarization of the infrared excitation. A marked steric effect is observed in which Cl atoms approaching perpendicular to the C-H stretch preferentially yield forward-scattered HCl(υ=1) product. On the other hand, the reaction is weakly dependent on the rotational quantum state of CH4(υ3=1,J), and on the rotational polarization. The data are consistent with a model that has a widely open ``cone of acceptance'' in which the impact parameter controls the internal-state and scattering distributions of the HCl product.