Vibronic Coupling Effects in the Photoelectron Spectrum of Ozone: A Coupled-Cluster Approach.

One of the most important areas of application for equation-of-motion coupled-cluster (EOM-CC) theory is the prediction, simulation, and analysis of various types of electronic spectra. In this work, the EOM-CC method for ionized states, known as EOM-IP-CC, is applied to the closely lying and coupled pair of states of the ozone cation─ and ─using highly accurate treatments including up to the full single, double, triple, and quadruple excitations (EOM-IP-CCSDTQ). Combined with a venerable and powerful method for calculating vibronic spectra from the Hamiltonian produced by EOM-IP-CC calculations, the simulations yield a spectrum that is in good agreement with the photoelectron spectrum of ozone.

Spectroscopy and Two-Photon Dissociation of Jet-Cooled Pyruvic Acid.

The UV photodissociation of pyruvic acid (PA) is studied in molecular beams using time-of-flight (TOF) mass spectroscopy and time-sliced velocity map imaging (VMI) following excitation to the first absorption band (S ← S) at 330-380 nm. CHCO, HOCO, CO, CH, and H are detected as photodissociation products. The photofragment yield (PFY) spectrum of the H product is recorded at 350-380 nm in He and Ar carrier gases.

Vibrational predissociation of the phenol-water dimer: a view from the water.

The vibrational predissociation (VP) dynamics of the phenol-water (PhOH-HO) dimer were studied by detecting HO fragments and using velocity map imaging (VMI) to infer the internal energy distributions of PhOH cofragments, pair-correlated with selected rotational levels of the HO fragments. Following infrared (IR) laser excitation of the hydrogen-bonded OH stretch fundamental of PhOH (Pathway 1) or the asymmetric OH stretch localized on HO (Pathway 2), dissociation to HO + PhOH was observed. HO fragments were monitored state-selectively by using 2+1 Resonance-Enhanced Multiphoton Ionization (REMPI) combined with time-of-flight mass spectrometry (TOF-MS).

Electronic Structure and Rydberg-Core Interactions in Hydroxycarbene and Methylhydroxycarbene.

Vertical and adiabatic excitation energies and oscillator strengths for valence and Rydberg states of hydroxycarbene (HCOH) and methylhydroxycarbene (CHCOH) are reported. The electronic properties were computed with equation-of-motion coupled-cluster methods with single and double substitution methods (EOM-CCSD) and the aug-cc-pVTZ basis set. The states' characters were analyzed by plotting natural transition orbitals (NTOs).

Predissociation dynamics of the HCl-(HO) tetramer: An experimental and theoretical investigation.

The cyclic HCl-(HO) tetramer is the largest observed neutral HCl-(HO) cluster. The vibrational predissociation of HCl-(HO) is investigated by theory, quasiclassical trajectory (QCT) calculations, and experiment, following the infrared excitation of the hydrogen-bonded OH-stretch fundamental. The energetically possible dissociation pathways are HCl + (HO) (Pathway 1) and HO + HCl-(HO) (Pathway 2).

Photoinitiated Dynamics in Amorphous Solid Water via Nanoimprint Lithography.

Laser pulses that act on fragile samples often alter them irreversibly, motivating single-pulse data collection. Amorphous solid water (ASW) is a good example. In addition, neither well-defined paths for molecules to travel through ASW nor sufficiently small samples to enable molecular dynamics modeling have been achieved.

Vibrational Predissociation of the HCl-(HO) Tetramer.

The vibrational predissociation of the HCl-(HO) tetramer, the largest HCl-(HO) cluster for which HCl is not predicted to be ionized, is reported. This work focuses on the predissociation pathway giving rise to HO + HCl-(HO) following IR laser excitation of the H-bonded OH stretch fundamental. HO fragments are monitored state selectively by 2 + 1 resonance-enhanced multiphoton ionization (REMPI) combined with time-of-flight mass spectrometry (TOF-MS).

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.

Experimental and theoretical investigations of energy transfer and hydrogen-bond breaking in small water and HCl clusters.

Water is one of the most pervasive molecules on earth and other planetary bodies; it is the molecule that is searched for as the presumptive precursor to extraterrestrial life. It is also the paradigm substance illustrating ubiquitous hydrogen bonding (H-bonding) in the gas phase, liquids, crystals, and amorphous solids. Moreover, H-bonding with other molecules and between different molecules is of the utmost importance in chemistry and biology.

Imaging studies of excited and dissociative States of hydroxymethylene produced in the photodissociation of the hydroxymethyl radical.

Rotational, vibrational, and electronic states of formaldehyde and cis-hydroxymethylene products generated in the photodissociation of the hydroxymethyl radical are investigated by sliced velocity map imaging (SVMI) following excitation of the radical to its 3px and 3pz Rydberg states. SVMI of H and D photofragments is essential in these studies because it allows zooming in on low-velocity regions of the images where small threshold signals can be identified. With CH2OD precursors, formaldehyde and hydroxymethylene products are examined separately by monitoring D and H, respectively.

Experiment and theory elucidate the multichannel predissociation dynamics of the HCl trimer: breaking up is hard to do.

The breaking of hydrogen bonds in molecular systems has profound effects on liquids, e.g., water, biomolecules, e.

Accessing multiple conical intersections in the 3s and 3p(x) photodissociation of the hydroxymethyl radical.

The photodissociation dynamics of the hydroxymethyl radical (CH2OH, CH2OD, and CD2OD) following excitation to the 3s and 3p(x) Rydberg states is studied using time-sliced velocity map imaging of hydrogen photofragments. Dissociation takes place on the ground potential energy surface reached via conical intersections from the excited states, and formaldehyde and hydrxymethylene are identified as reaction products. The major product, formaldehyde, has a bimodal internal energy distribution.

Improved sliced velocity map imaging apparatus optimized for H photofragments.

Time-sliced velocity map imaging (SVMI), a high-resolution method for measuring kinetic energy distributions of products in scattering and photodissociation reactions, is challenging to implement for atomic hydrogen products. We describe an ion optics design aimed at achieving SVMI of H fragments in a broad range of kinetic energies (KE), from a fraction of an electronvolt to a few electronvolts. In order to enable consistently thin slicing for any imaged KE range, an additional electrostatic lens is introduced in the drift region for radial magnification control without affecting temporal stretching of the ion cloud.

Experimental and theoretical investigations of the dissociation energy (D0) and dynamics of the water trimer, (H2O)3.

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 (D0) for the (H2O)3 → H2O + (H2O)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, D0 = 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 .

Experimental and theoretical investigations of energy transfer and hydrogen-bond breaking in the water dimer.

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.

Communication: determination of the bond dissociation energy (D0) of the water dimer, (H2O)2, by velocity map imaging.

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 the C̃ (1)B(1) (000) ← X̃ (1)A(1) (000 and 010) transitions.

Imaging H2O photofragments in the predissociation of the HCl-H2O hydrogen-bonded dimer.

The state-to-state vibrational predissociation (VP) dynamics of the hydrogen-bonded 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 + 1 REMPI via the C (1)B(1) (000) ← X (1)A(1) (000) transition.

Imaging the state-specific vibrational predissociation of the hydrogen chloride-water hydrogen-bonded dimer.

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)Delta(2) <-- X (1)Sigma(+) and V (1)Sigma(+) <-- X (1)Sigma(+) transitions.

Can the fragmentation of hydrogen-bonded dimers be predicted: predissociation of C2H2-HX.

HX rotational state distributions following vibrational predissociation (VP) of C(2)H(2)-HX (X = Cl, F, O) dimers are predicted by expressing the predissociation process as the joint probability of rovibrational excitation in the fragments following "internal collision" in the vibrationally excited dimer. Calculations of these joint probabilities for the T-shaped dimers of acetylene with HCl, DCl, HF, and OH using the angular momentum (AM) method reproduce experimental distributions with reasonable accuracy. In dimers of this complex, many different pathways for the disposal of initial energy and momentum exist in principle.

Imaging the state-specific vibrational predissociation of the ammonia-water hydrogen-bonded dimer.

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 resonance-enhanced 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 B1E" <-- X1A1' transition.

Multiphoton ionization and dissociation of diazirine: a theoretical and experimental study.

Multiphoton ionization and dissociation processes in diazirine have been studied experimentally via 304-325 nm two-photon absorption and theoretically by using the EOM-CCSD and B3LYP methods. The electronic structure calculations identified two excited valence states and four Rydberg states in the region 4.0-8.