Development of the Time-Independent Methods for the Cl + H/F + HD Reaction Using Hyper-Spherical Coordinates Including (Full) Spin-Orbit Characteristics.

Recently, a combined study of high-resolution molecular crossed beam experiment and accurate full-dimensional time-dependent theory, including full spin-orbit characteristics on the effect of electronic spin and orbital angular momenta in the F + HD reaction, was reported by some of us, focusing on the partial wave resonance phenomenon ( 936-940). It revealed that the time-dependent theory could explain all of the details observed in the high-resolution experiment. Here, we develop two time-independent close-coupling methods using hyperspherical coordinates, including the two-state model, where only a part of the spin-orbit characteristics is considered, and the six-state model, where the full spin-orbit characteristics is considered.

Rotational energy transfer kinetics of optically centrifuged CO molecules investigated through transient IR spectroscopy and master equation simulations.

A combined experimental and theoretical study of quantum state-resolved rotational energy transfer kinetics of optically centrifuged CO molecules is presented. In the experiments, inverted rotational distributions of CO in rotational states up to = 80 were prepared using two different optical centrifuge traps, one with the full spectral bandwidth of the optical centrifuge pulses, and one with reduced bandwidth. The relaxation kinetics of the high- tail of the inverted distribution from each optical trap was determined based on high-resolution transient IR absorption measurements.

Enhanced reactivity of fluorine with para-hydrogen in cold interstellar clouds by resonance-induced quantum tunnelling.

Chemical reactions are important in the evolution of low-temperature interstellar clouds, where the quantum tunnelling effect becomes significant. The F + para-H → HF + H reaction, which has a significant barrier of 1.8 kcal mol, is an important source of HF in interstellar clouds; however, the dynamics of this quantum-tunnelling-induced reactivity at low temperature is unknown.

Accurate characterization of the lowest triplet potential energy surface of SO with a coupled cluster method.

The near-equilibrium potential energy surface (PES) of the ã B state of SO is developed from explicitly correlated spin-unrestricted coupled cluster calculations with single, double, and perturbative triple excitations with an augmented triple-zeta correlation-consistent basis set. The lowest-lying ro-vibrational energy levels of several sulfur isotopologues have been determined using this PES. It is shown that the new ab initio PES provides a much better description of the low-lying vibrational states than a previous PES determined at the multi-reference configuration interaction level.

Experimental and theoretical investigation of the temperature dependent electronic quenching of O(D) atoms in collisions with Kr.

The kinetics and dynamics of the collisional electronic quenching of O(D) atoms by Kr have been investigated in a joint experimental and theoretical study. The kinetics of quenching were measured over the temperature range 50-296 K using the Laval nozzle method. O(D) atoms were prepared by 266 nm photolysis of ozone, and the decay of the O(D) concentration was monitored through vacuum ultraviolet fluorescence at 115.

Chemical Control and Spectral Fingerprints of Electronic Coupling in Carbon Nanostructures.

The optical and electronic properties of atomically thin materials such as single-walled carbon nanotubes and graphene are sensitively influenced by substrates, the degree of aggregation, and the chemical environment. However, it has been experimentally challenging to determine the origin and quantify these effects. Here we use time-dependent density-functional-theory calculations to simulate these properties for well-defined molecular systems.

Final State Resolved Quantum Predissociation Dynamics of SO(C̃B) and Its Isotopomers via a Crossing with a Singlet Repulsive State.

The fragmentation dynamics of predissociative SO(C̃B) is investigated on an accurate adiabatic potential energy surface (PES) determined from high level ab initio data. This singlet PES features non-C equilibrium geometries for SO, which are separated from the SO(X̃Σ) + O(P) dissociation limit by a barrier resulting from a conical intersection with a repulsive singlet state. The ro-vibrational state distribution of the SO fragment is determined quantum mechanically for many predissociative states of several sulfur isotopomers of SO.

First-principles C band absorption spectra of SO and its isotopologues.

The low-energy wing of the C∼B21←X∼A absorption spectra for SO in the ultraviolet region is computed for the 32S,S,S and S isotopes, using the recently developed ab initio potential energy surfaces (PESs) of the two electronic states and the corresponding transition dipole surface. The state-resolved absorption spectra from various ro-vibrational states of SO(X∼A) are computed. When contributions of these excited ro-vibrational states are included, the thermally averaged spectra are broadened but maintain their key characters.

The interaction of NO(XΠ) with H: Ab initio potential energy surfaces and bound states.

We determine from first principles two sets of four-dimensional diabatic potential energy surfaces (PES's) for the interaction of NO(XΠ) with H, under the assumption of fixed NO and H bond distances. The first set of PES's was computed with the explicitly correlated multi-reference configuration interaction method [MRCISD-F12 + Q(Davidson)], and the second set with an explicitly correlated, coupled-cluster method [RCCSD(T)-F12a] with the geometry scan limited to geometries possessing a plane of symmetry. The calculated PES's are then fit to an analytical form suitable for bound state and scattering calculations.

Photoabsorption Assignments for the C̃B ← X̃A Vibronic Transitions of SO, Using New Ab Initio Potential Energy and Transition Dipole Surfaces.

The high resolution spectroscopy of the SO molecule is of great topical interest, in a wide variety of contexts ranging from origins of higher life, to astrophysics of the interstellar medium, to environmental chemistry. In particular, the C̃B ← X̃A UV photoabsorption spectrum has received considerable attention. This spectrum exhibits a highly regular progression of ∼20 or so strong peaks, spaced roughly 350 cm apart, which is comparable to the C̃B bending vibrational frequency.

Accurate transport properties for O(P)-H and O(P)-H.

Transport properties for collisions of oxygen atoms with hydrogen atoms and hydrogen molecules have been computed by means of time-independent quantum scattering calculations. For the O(P)-H(S) interaction, potential energy curves for the four OH electronic states emanating from this asymptote were computed by the internally-contracted multi-reference configuration interaction method, and the R-dependent spin-orbit matrix elements were taken from Parlant and Yarkony [J. Chem.

New ab initio adiabatic potential energy surfaces and bound state calculations for the singlet ground X̃(1)A1 and excited C̃(1)B2(2(1)A(')) states of SO2.

We report new and more accurate adiabatic potential energy surfaces (PESs) for the ground X̃(1)A1 and electronically excited C̃(1)B2(2(1)A(')) states of the SO2 molecule. Ab initio points are calculated using the explicitly correlated internally contracted multi-reference configuration interaction (icMRCI-F12) method. A second less accurate PES for the ground X̃ state is also calculated using an explicitly correlated single-reference coupled-cluster method with single, double, and non-iterative triple excitations [CCSD(T)-F12].

State-Specific Collision Dynamics of Molecular Super Rotors with Oriented Angular Momentum.

An optical centrifuge pulse drives carbon dioxide molecules into ultrahigh rotational states with rotational frequencies of ω ≈ 32 THz based on the centrifuge frequency at the full width at half-maximum of the spectral chirp. High-resolution transient IR absorption spectroscopy is used to measure the time-evolution of translational and rotational energy for a number of states in the range of J = 0-100 at a sample pressure of 5-10 Torr. Transient Doppler profiles show that the products of super rotor collisions contain substantial amounts of translational energy, with J-dependent energies correlating to a range of ΔJ propensities.

Inelastic Scattering of NO by Kr: Rotational Polarization over a Rainbow.

We use molecular beams and ion imaging to determine quantum state resolved angular distributions of NO radicals after inelastic collision with Kr. We also determine both the sense and the plane of rotation (the rotational orientation and alignment, respectively) of the scattered NO. By full selection and then detection of the quantum parity of the NO molecule, our experiment is uniquely sensitive to quantum interference.

Electronic quenching of O((1)D) by Xe: Oscillations in the product angular distribution and their dependence on collision energy.

The dynamics of the O((1)D) + Xe electronic quenching reaction was investigated in a crossed beam experiment at four collision energies. Marked large-scale oscillations in the differential cross sections were observed for the inelastic scattering products, O((3)P) and Xe. The shape and relative phases of the oscillatory structure depend strongly on collision energy.

Theoretical investigation of the dynamics of O((1)D→(3)P) electronic quenching by collision with Xe.

We present the quantum close-coupling treatment of spin-orbit induced transitions between the (1)D and (3)P states of an atom in collisions with a closed-shell spherical partner. In the particular case of O colliding with Xe, we used electronic structure calculations to compute the relevant potential energy curves and spin-orbit coupling matrix elements. We then carried out quantum scattering calculations of integral and differential quenching cross sections as functions of the collision energy.

Resonances in rotationally inelastic scattering of NH3 and ND3 with H2.

We present theoretical studies on the scattering resonances in rotationally inelastic collisions of NH3 and ND3 molecules with H2 molecules. We use the quantum close-coupling method to compute state-to-state integral and differential cross sections for the NH3/ND3-H2 system for collision energies between 5 and 70 cm(-1), using a previously reported potential energy surface [Maret et al., Mon.

REACTION DYNAMICS. Spectroscopic observation of resonances in the F + H2 reaction.

Photodetachment spectroscopy of the FH2(-) and FD2(-) anions allows for the direct observation of reactive resonances in the benchmark reaction F + H2 → HF + H. Using cooled anion precursors and a high-resolution electron spectrometer, we observe several narrow peaks not seen in previous experiments. Theoretical calculations, based on a highly accurate F + H2 potential energy surface, convincingly assign these peaks to resonances associated with quasibound states in the HF + H and DF + D product arrangements and with a quasibound state in the transition state region of the F + H2 reaction.

Rotationally inelastic scattering of OH by molecular hydrogen: Theory and experiment.

We present an experimental and theoretical investigation of rotationally inelastic transitions of OH, prepared in the X(2)Π, v = 0, j = 3/2 F1f level, in collisions with molecular hydrogen (H2 and D2). In a crossed beam experiment, the OH radicals were state selected and velocity tuned over the collision energy range 75-155 cm(-1) using a Stark decelerator. Relative parity-resolved state-to-state integral cross sections were determined for collisions with normal and para converted H2.

A finite-element visualization of quantum reactive scattering. II. Nonadiabaticity on coupled potential energy surfaces.

This is the second in a series of papers detailing a MATLAB based implementation of the finite element method applied to collinear triatomic reactions. Here, we extend our previous work to reactions on coupled potential energy surfaces. The divergence of the probability current density field associated with the two electronically adiabatic states allows us to visualize in a novel way where and how nonadiabaticity occurs.

Theoretical investigation of the relaxation of the bending mode of CH₂(X̃) by collisions with helium.

We have earlier determined the dependence on the bending angle of the interaction of the methylene radical (CH2) in its X̃³B₁ state with He [L. Ma, P. J.

The interaction of OH(X²Π) with H₂: ab initio potential energy surfaces and bound states.

For the interaction of OH(X(2)Π) with H2, under the assumption of fixed OH and H2 bond distances, we have determined two new sets of four-dimensional ab initio potential energy surfaces (PES's). The first set of PES's was computed with the multi-reference configuration interaction method [MRCISD+Q(Davidson)], and the second set with an explicitly correlated coupled cluster method [RCCSD(T)-F12a] sampling the subset of geometries possessing a plane of symmetry. Both sets of PES's are fit to an analytical form suitable for bound state and scattering calculations.

Theoretical investigation of intersystem crossing between the ã¹A₁ and X³B₁ states of CH₂ induced by collisions with helium.

Collisional energy transfer between the ground (X³B₁) and first excited (ã¹A₁) states of CH2 is facilitated by strong mixing of the rare pairs of accidentally degenerate rotational levels in the ground vibrational manifold of the [Formula: see text] state and the (020) and (030) excited bending vibrational manifolds of the X state. The simplest model for this process involves coherent mixing of the scattering T-matrix elements associated with collisional transitions within the unmixed ã and X states. From previous calculations in our group, we have determined cross sections and room-temperature rate constants for intersystem crossing of CH2 by collision with He.

Transport properties for systems with deep potential wells: H + O2.

Transport properties for collisions of the oxygen molecule with hydrogen atoms are computed by means of quantum scattering calculations. Because two potential energy surfaces (PESs) arise from the interaction of H(2S) with O2(X3Σg+), namely 2A″ and 4A″, collision integrals were computed using both PESs and then averaged with weighting by their respective spin multiplicities. A PES for the 4A″ state was computed for the interaction of O2, frozen at its equilibrium internuclear separation, with a hydrogen atom, using a coupled-cluster method that includes all single and double excitations as well as perturbative contributions of connected triple excitation.