Sensitive Low-Recoil VUV 1 + 1' REMPI Detection of ND.

In molecular beam scattering experiments, an important technique for measuring product energy and angular distributions is velocity map imaging following photoionization of one or more scattered species. For studies with cold molecular beams, the ultimate resolution of such a study is often limited by the product detection process. When state-selective ionization detection is used, excess energy from the ionization step can transfer to kinetic energy in the target molecular ion-electron pair, resulting in measurable cation recoil.

Multiphoton Ionization/Dissociation of Molecular Sulfur S in the UV Region.

The multiphoton ionization/dissociation dynamics of molecular sulfur (S) in the ultraviolet range of 205-300 nm is studied using velocity map ion imaging (VMI). In this one-color experiment, molecular sulfur (S) is generated in a pulsed discharge and then photodissociated by UV radiation. At the three-photon level, superexcited states are accessed via two different resonant states: the Σ (' = 8-11) valence states at the one-photon level and a Rydberg state at the two-photon level.

Vibrational state-specific nonadiabatic photodissociation dynamics of OCS+ via A2Π1/2 (ν1 0 ν3) states.

The identification and analysis of quantum state-specific effects can significantly deepen our understanding of detailed photodissociation dynamics. Here, we report an experimental investigation on the vibrational state-mediated photodissociation of the OCS+ cation via the A2Π1/2 (ν1 0 ν3) states by using the velocity map ion imaging technique over the photolysis wavelength range of 263-294 nm. It was found that the electronically excited S+ product channel S+(2Du) + CO (X1Σ+) was significantly enhanced when the ν1 and ν3 vibrational modes were excited.

Imaging rotational energy transfer: comparative stereodynamics in CO + N and CO + CO inelastic scattering.

State-to-state rotational energy transfer in collisions of ground ro-vibrational state CO molecules with N molecules has been studied using the crossed molecular beam method under kinematically equivalent conditions used for CO + CO rotationally inelastic scattering described in a previously published report (Sun , , 2020, , 307-309). The collisionally excited CO molecule products are detected by the same (1 + 1' + 1'') VUV (Vacuum Ultra-Violet) resonance enhanced multiphoton ionization scheme coupled with velocity map ion imaging. We present differential cross sections and scattering angle resolved rotational angular momentum alignment moments extracted from experimentally measured CO + N scattering images and compare them with theoretical predictions from quasi-classical trajectories (QCT) on a newly calculated CO-N potential energy surface (PES).

Vacuum ultraviolet photodissociation dynamics of OCS via the F Rydberg state: The O (3PJ=2,1,0) product channels.

We study the vacuum ultraviolet (VUV) photodissociation dynamics of carbonyl sulfide (OCS) by using the time sliced velocity map ion imaging technique. Experimental images of the dissociative O (3PJ=0,1,2) products were acquired at five VUV photolysis wavelengths from 133.26 to 139.

Disentangling Multiphoton Ionization and Dissociation Channels in Molecular Oxygen Using Photoelectron-Photoion Coincidence Imaging.

Multiphoton excitation of molecular oxygen in the 392-408 nm region is studied using a tunable femtosecond laser coupled with a double velocity map imaging photoelectron-photoion coincidence spectrometer. The laser intensity is held at ≤∼1 TW/cm to ensure excitation in the perturbative regime, where the possibility of resonance enhanced multiphoton ionization (REMPI) can be investigated. O production is found to be resonance enhanced around 400 nm via three-photon excitation to the e'Δ( = 0) state, similar to results from REMPI studies using nanosecond dye lasers.

Photodissociation Dynamics of Astrophysically Relevant Propyl Derivatives (CHX; X = CN, OH, HCO) at 157 nm Exploiting an Ultracompact Velocity Map Imaging Spectrometer: The (Iso)Propyl Channel.

The photodissociation dynamics of astrophysically relevant propyl derivatives (CHX; X = CN, OH, HCO) at 157 nm exploiting an ultracompact velocity map imaging (UVMIS) setup has been reported. The successful operation of UVMIS allowed the exploration of the 157 nm photodissociation of six (iso)propyl systems─-propyl cyanide (CHCN), -propyl alcohol (CHOH), and (iso)butanal (CHCHO)─to explore the CH loss channel. The distinct center-of-mass translational energy distributions for the -CHX (X= CN, OH, HCO) could be explained through preferential excitation of the low frequency C-H bending modes of the formyl moiety compared to the higher frequency stretching of the cyano and hydroxy moieties.

Dynamics and vector correlations of vacuum ultraviolet (VUV) photodissociation of CO at 155 nm.

In this work, the CO Vacuum Ultraviolet (VUV) photodissociation dynamics of the dominant O(D) channel near 155 nm have been studied using Velocity Map Imaging (VMI) technique. Correlations among the transition dipole moment of the parent molecule, recoil velocity vector and rotational angular momentum vector of the photofragments were extracted from the anisotropic angular distributions of the images. The vector correlations extracted indicated a picture of photodissociation mainly the excited 2A' (A) state.

Femtosecond 2 + 1 Resonance-Enhanced Multiphoton Ionization Spectroscopy of the -State in Molecular Oxygen.

Coincidence electron-cation imaging is used to characterize the multiphoton ionization of O via the = 4,5 levels of the 3s(Π) Rydberg state. A tunable 100 fs laser beam operating in the 271-263 nm region is found to cause a nonresonant ionization across this wavelength range, with an additional resonant ionization channel only observed when tuned to the Π( = 5) level. A distinct 3s → p wave character is observed in the photoelectron angular distribution for the = 5 channel when on resonance.

Molecular square dancing in CO-CO collisions.

Knowledge of rotational energy transfer (RET) involving carbon monoxide (CO) molecules is crucial for the interpretation of astrophysical data. As of now, our nearly perfect understanding of atom-molecule scattering shows that RET usually occurs by only a simple "bump" between partners. To advance molecular dynamics to the next step in complexity, we studied molecule-molecule scattering in great detail for collision between two CO molecules.

Imaging inelastic scattering of CO with argon: polarization dependent differential cross sections.

Rotationally inelastic scattering of carbon monoxide (CO) with Argon at a collision energy of 700 cm-1 has been investigated by measuring polarization dependent differential scattering cross sections (PDDCSs) for rotationally excited CO molecules using a crossed molecular beam apparatus coupled with velocity-map ion imaging. A simple and robust (1 + 1' + 1'') VUV (Vacuum Ultra-Violet) REMPI (Resonance Enhanced Multi Photon Ionization) scheme is used and images are obtained by setting the VUV light polarization direction parallel or perpendicular to the scattering plane. Clear differences between the images for the two polarizations are observed, indicating strong collision induced alignment of the rotational angular momentum of scattered CO.

Collision-induced absorption between O-CO for the aΔ (v = 1) ← XΣ (v = 0) transition of molecular oxygen at 1060 nm.

Collision-induced absorption between O2 and CO2 molecules associated with the a1Δg (v = 1) ← X3Σ-g (v = 0) band of oxygen around 1060 nm was measured using cavity ring-down spectroscopy. The lineshape for this transition is measured for the first time, and the integrated cross-section is found to be smaller than the only previous report. For pure oxygen, we find an integrated absorption value of (2.

Detection of the O A'Δ Herzberg III state by photofragment imaging.

Photofragment imaging is shown to provide a sensitive method for detection of the O2 A'3Δu Herzberg III state using a one-laser dissociation/O(1D) resonance enhanced multiphoton ionization (REMPI) scheme with a focused nanosecond dye laser beam tuned to 203.8 or 205.2 nm, combined with velocity map imaging of the atomic oxygen photofragment.

Communication: State-to-state inelastic scattering of interstellar O with H.

Molecular oxygen (O) is predicted to be a major reservoir of elemental oxygen in dense interstellar molecular clouds. However, the abundance of O derived from astronomical observations is much lower than expected. Solving the discrepancies between models and observations requires a review of the chemistry and collisional excitation of O in space.

Publisher Correction: O-O and O-N collision-induced absorption mechanisms unravelled.

In the version of this Article originally published, Figures 3 and 4 were erroneously swapped, this has been corrected in all versions of the Article.

O-O and O-N collision-induced absorption mechanisms unravelled.

Collision-induced absorption is the phenomenon in which interactions between colliding molecules lead to absorption of light, even for transitions that are forbidden for the isolated molecules. Collision-induced absorption contributes to the atmospheric heat balance and is important for the electronic excitations of O that are used for remote sensing. Here, we present a theoretical study of five vibronic transitions in O-O and O-N, using analytical models and numerical quantum scattering calculations.

Perspective: Advanced particle imaging.

Since the first ion imaging experiment [D. W. Chandler and P.

Imaging state-to-state reactive scattering in the Ar + H charge transfer reaction.

The charge transfer reaction of Ar with H and D has been investigated in an experiment combining crossed beams with three-dimensional velocity map imaging. Angle-differential cross sections for two collision energies have been obtained for both neutral species. We find that the product ions are highly internally excited.

State-to-State Inelastic Scattering of O2 with Helium.

Molecular oxygen (O2) is extremely important for a wide variety of processes on and outside Earth. Indeed, O2–He collisions are crucial to model O2 abundance in space or to create ultracold O2 molecules. A crossed molecular beam experiment to probe rotational excitation of O2 due to helium collisions at energies of 660 cm–1 is reported.

Inelastic Scattering of CO with He: Polarization Dependent Differential State-to-State Cross Sections.

A joint theoretical and experimental study of state-to-state rotationally inelastic polarization dependent differential cross sections (PDDCSs) for CO (v = 0, j = 0, 1, 2) molecules colliding with helium is reported for collision energies of 513 and 840 cm(-1). In a crossed molecular beam experiment, velocity map imaging (VMI) with state-selective detection by (2 + 1) and (1 + 1') resonance enhanced multiphoton ionization (REMPI) is used to probe rotational excitation of CO due to scattering. By taking account of the known fractions of the j = 0, 1, and 2 states of CO in the rotationally cold molecular beam (Trot ≈ 3 K), close-coupling theory based on high-quality ab initio potential energy surfaces for the CO-He interaction is used to simulate the differential cross sections for the mixed initial states.

Analysis of velocity-mapped ion images from high-resolution crossed-beam scattering experiments: a tutorial review.

A Stark decelerator produces beams of molecules with high quantum state purity, and small spatial, temporal and velocity spreads. These tamed molecular beams are ideally suited for high-resolution crossed beam scattering experiments. When velocity map imaging is used, the Stark decelerator allows the measurement of scattering images with unprecedented radial sharpness and angular resolution.

Singlet oxygen photogeneration from X-O₂ van der Waals complexes: double spin-flip vs. charge-transfer mechanism.

The channel of singlet oxygen O2((1)Δg) photogeneration from van der Waals complexes of oxygen X-O2 has been investigated to discriminate between two possible mechanisms based on charge-transfer (CT) or double spin-flip (DSF) transitions. The results obtained in this work for complexes with X = ethylene C2H4, 1,3-butadiene C4H6, deuterated methyl iodide CD3I, benzene C6H6 and water H2O and for those investigated previously indicate the DSF mechanism as a source of singlet oxygen. The formation of O2((1)Δg) is observed only when the energy of exciting quantum is sufficient for DSF transition.

The Jahn-Teller effect in the presence of partial isotopic substitution: the B̃(1)E'' state of NH2D and NHD2.

Rotationally resolved resonance enhanced multiphoton ionisation spectra of the B̃(1)E'' state of NH2D are presented and analysed. The analysis indicates a small (34.9 cm(-1)) lifting of the vibronic degeneracy of the zero point level, approximately equal in sign but opposite in magnitude to the splitting observed in NHD2 in previous work.