Correlated Product Distributions in the Photodissociation of ̃ State NO-CH and NO-N van der Waals Complexes.

This paper reports correlated product distributions for dissociation of the van der Waals complexes NO-CH and NO-N on their ̃ state surfaces, providing detailed data sets against which calculations can be benchmarked. NO-CH dissociation strongly favors small changes in the CH angular momentum, with Δ = 0 and 1 providing the bulk of the products. Conversely, the associated NO products show little constraint in terms of the rotational angular momentum transfer, with the full range of energetically accessible angular momentum states populated, although the distributions show minima.

Strong Torsion-Vibration Interaction in -Methylpyrrole Observed by Far-Infrared Spectroscopy.

An interaction between methyl torsion and the low-lying out-of-plane methyl wag vibration has been observed in toluene, -fluorotoluene, and -fluorotoluene, contravening the traditional assumption used when analyzing spectra that methyl torsion can be treated independently of the small-amplitude vibrations. When a methyl group is attached to a planar frame, out-of-plane methyl wag vibrations always occur, and hence this type of interaction between methyl torsion and vibration is potentially extensive. To probe whether this coupling occurs beyond toluene and its derivatives, we have studied the far-infrared absorption band for the out-of-plane methyl wagging mode in -methylpyrrole.

Torsion-vibration interactions determined from (far) infrared spectra.

Observations of the torsional and low-lying vibrational-torsional states of toluene, p-fluorotoluene, and m-fluorotoluene using the technique of two dimensional laser induced fluorescence (2D-LIF) have revealed interactions between the methyl torsion and low frequency out-of-plane methyl wagging vibration. These interactions can change the values of constants extracted from the analysis of rotational spectra, which usually assume that the large amplitude torsional motion can be treated independent of the small amplitude vibrations. Since out-of-plane methyl wagging modes will be present whenever a methyl group is attached to a planar frame, this type of torsion-vibration interaction is potentially widespread; it is thus important to establish the extent and strength of this type of interaction.

Continuous flow vortex fluidic-mediated exfoliation and fragmentation of two-dimensional MXene.

MXene (TiCT ) is exfoliated in a vortex fluidic device (VFD), as a thin film microfluidic platform, under continuous flow conditions, down to 3 nm thin multi-layered two-dimensional (2D) material, as determined using AFM. The optimized process, under an inert atmosphere of nitrogen to avoid oxidation of the material, was established by systematically exploring the operating parameters of the VFD, along with the concentration of the dispersed starting material and the choice of solvent, which was a 1 : 1 mixture of isopropyl alcohol and water. There is also some fragmentation of the 2D material into nanoparticles 68 nm in diameter.

Dynamic thin film mediated slicing of boron nitride nanotubes.

A method has been developed to slice boron nitride nanotubes BNNTs under continuous flow in a vortex fluidic device (VFD), along with a method to partially purify the as received BNNT containing material. The latter involves heating the BNNTs to 600 °C followed by dispersing in a 1 : 3 isopropyl alcohol (IPA) and water mixture at 100 °C. The VFD mediated slicing of the BNNTs comprises irradiating the rapidly rotating glass tube (20 mm OD) with a pulsed Nd:YAG laser.

A strong interaction between torsion and vibration in S and Sm-fluorotoluene.

We report results of a two dimensional laser induced fluorescence study of torsional states, low frequency vibrations, and combinations of torsion with low frequency vibration in m-fluorotoluene up to 560 cm in S and 350 cm in S. Evidence is presented for interactions between torsion and low frequency vibrations in both S and S, demonstrating that the coupling of torsion and vibration observed previously in toluene and p-fluorotoluene extends to a molecule with a threefold torsional barrier. This barrier is low in S (20 cm) and modest in S (116 cm).

Pervasive interactions between methyl torsion and low frequency vibrations in S and S-fluorotoluene.

We report two dimensional laser induced fluorescence spectral images exploring the lower torsion-vibration manifolds in S ( < 560 cm) and S ( < 420 cm) -fluorotoluene. Analysis of the images reveals strong torsion-vibration interactions and provides an extensive set of torsion-vibration state energies in both electronic states (estimated uncertainty ±0.2 cm), which are fit to determine key constants including barrier heights, torsional constants, and torsion-vibration interaction constants.

A "circularisation" method to repair deformations and determine the centre of velocity map images.

A problem besetting the analysis of velocity map images, particularly those of photoelectrons, is the presence of distortions that cause the features in the image to deviate from circularity, leading to a loss of resolution in the spectrum extracted. A method is presented to repair such distortions based on fitting the angular behaviour of each of the ring structures to a trigonometric expansion. The repair function allows the intensity at any value of radius and angle to be mapped to a new position that removes the distortion and returns the features to circular.

First spectroscopic observation of gold(i) butadiynylide: Photodetachment velocity map imaging of the AuC4H anion.

The velocity map imaging technique was used in the investigation of gold(i) butadiynylide, AuC4H(-), with images recorded at two excitation wavelengths. The resultant photodetachment spectra show a well defined vibrational progression in the neutral with an energy spacing of 343 ± 3 cm(-1). The adiabatic electron affinity was determined to be 1.

Fluid dynamic lateral slicing of high tensile strength carbon nanotubes.

Lateral slicing of micron length carbon nanotubes (CNTs) is effective on laser irradiation of the materials suspended within dynamic liquid thin films in a microfluidic vortex fluidic device (VFD). The method produces sliced CNTs with minimal defects in the absence of any chemical stabilizers, having broad length distributions centred at ca 190, 160 nm and 171 nm for single, double and multi walled CNTs respectively, as established using atomic force microscopy and supported by small angle neutron scattering solution data. Molecular dynamics simulations on a bent single walled carbon nanotube (SWCNT) with a radius of curvature of order 10 nm results in tearing across the tube upon heating, highlighting the role of shear forces which bend the tube forming strained bonds which are ruptured by the laser irradiation.

Rotational and angular distributions of NO products from NO-Rg (Rg = He, Ne, Ar) complex photodissociation.

We present the results of an investigation into the rotational and angular distributions of the NO à state fragment following photodissociation of the NO-He, NO-Ne, and NO-Ar van der Waals complexes excited via the à ← X̃ transition. For each complex, the dissociation is probed for several values of Ea, the available energy above the dissociation threshold. For NO-He, the Ea values probed were 59, 172, and 273 cm(-1); for NO-Ne they were 50 and 166 cm(-1); and for NO-Ar they were 44, 94, 194, and 423 cm(-1).

Torsion-vibration coupling in S1 toluene: Implications for IVR, the torsional barrier height, and rotational constants.

We have examined the S1←S0 transition of toluene in the region from the 0(0)(0) band to ∼210 cm(-1) above it. The spectrum reveals methyl rotor levels of 0(0) toluene up to m = 6 and of the lowest frequency vibration, 20(1), up to m = 4. The rotor levels of both 20(1) and 0(0) are perturbed by torsion-vibration coupling.

Direct observation of methyl rotor and vib-rotor states of S0 toluene: a revised torsional barrier due to torsion-vibration coupling.

We report a two dimensional, laser induced fluorescence study of the lowest 345 cm(-1) region of S0 toluene. Methyl rotor levels of 00 up to m = 6 and of 201 up to m = 4 are observed. The rotor levels of 00 and 201 have quite different energy spacings that are well fit by a model that includes strong torsion-vibration coupling between them.

Spectroscopic observation of gold-dicarbide: photodetachment and velocity map imaging of the AuC2 anion.

Photoelectron spectra following photodetachment of the gold dicarbide anion, AuC2(-), have been recorded using the velocity map imaging technique at several excitation wavelengths. The binding energy spectra show well-defined vibrational structure which, with the aid of computational calculations and Franck-Condon simulations, was assigned to a progression in the Au-C stretching mode, ν3. The experimental data indicate that the features in the spectrum correspond to a (2)A' ← (3)A' transition, involving states which we calculate to have bond angles ~147° but with a low barrier to linearity.

Methyl rotor dependent vibrational interactions in toluene.

The methyl rotor dependence of a three state Fermi resonance in S1 toluene at ∼460 cm(-1) has been investigated using two-dimensional laser induced fluorescence. An earlier time-resolved study has shown the Fermi resonance levels to have different energy spacings at the two lowest methyl rotor states, m = 0 and 1 [J. A.

The toluene-Ar complex: S0 and S1 van der Waals modes, changes to methyl rotation, and torsion-van der Waals vibration coupling.

The methyl rotor and van der Waals vibrational levels in the S1 and S0 states of toluene-Ar have been investigated by the technique of two-dimensional laser induced fluorescence (2D-LIF). The S0 van der Waals and methyl rotor levels are reported for the first time, while improved S1 values are presented. The correlations seen in the 2D-LIF images between the S0 and S1 states lead to a reassignment of key features in the S1 ← S0 excitation spectrum.

Intermolecular vibrations of fluorobenzene-Ar up to 130 cm(-1) in the ground electronic state.

Sixteen intermolecular vibrational levels of the S(0) state of the fluorobenzene-Ar van der Waals complex have been observed using dispersed fluorescence. The levels range up to ~130 cm(-1) in vibrational energy. The vibrational energies have been modelled using a complete set of harmonic and quartic anharmonic constants and a cubic anharmonic coupling between the stretch and long axis bend overtone that becomes near ubiquitous at higher energies.

Two-dimensional laser induced fluorescence spectroscopy of van der Waals complexes: fluorobenzene-Ar(n) (n = 1,2).

The technique of two-dimensional laser induced fluorescence (2D-LIF) spectroscopy has been used to observe the van der Waals complexes fluorobenzene-Ar and fluorobenzene-Ar(2) in the region of their S(1)-S(0) electronic origins. The 2D-LIF spectral images reveal a number of features assigned to the van der Waals vibrations in S(0) and S(1). An advantage of 2D-LIF spectroscopy is that the LIF spectrum associated with a particular species may be extracted from an image.

The binding energies of NO-Rg (Rg = He, Ne, Ar) determined by velocity map imaging.

We report velocity map imaging measurements of the binding energies, D(0), of NO-Rg (Rg = He, Ne, Ar) complexes. The X state binding energies determined are 3.0 ± 1.

Two dimensional laser induced fluorescence spectroscopy: a powerful technique for elucidating rovibronic structure in electronic transitions of polyatomic molecules.

We demonstrate the power of high resolution, two dimensional laser induced fluorescence (2D-LIF) spectroscopy for observing rovibronic transitions of polyatomic molecules. The technique involves scanning a tunable laser over absorption features in the electronic spectrum while monitoring a segment, in our case 100 cm(-1) wide, of the dispersed fluorescence spectrum. 2D-LIF images separate features that overlap in the usual laser induced fluorescence spectrum.

The dissociation of NO-Ar(A) from around threshold to 200 cm(-1) above threshold.

We report an investigation of the dissociation of A state NO-Ar at energies from 23 cm(-1) below the dissociation energy to 200 cm(-1) above. The NO product rotational distributions show population in states that are not accessible with the energy available for excitation from the NO ground state. This effect is observed at photon energies from below the dissociation energy up to approximately 100 cm(-1) above it.

A velocity map ion imaging study of difluorobenzene-water complexes: binding energies and recoil distributions.

The binding energies of the p-, m-, and o-difluorobenzene-H(2)O complexes have been measured by velocity map ion imaging to be 922+/-10, 945+/-10, and 891+/-4 cm(-1), respectively. The lack of variation provides circumstantial evidence for water binding to the three isomers via the same interaction, viz. an in-plane O-H.

Recoil energy distributions for dissociation of the van der Waals molecule p-difluorobenzene-Ar with 450-3000 cm(-1) excess energy.

Velocity map imaging has been used to measure the distributions of translational energy released in the dissociation of p-difluorobenzene-Ar van der Waals complexes from the 5(1), 3(1), 5(2), 3(1)5(1), 5(3), 3(2), and 3(2)5(1) states. These states span 818-3317 cm(-1) of vibrational energy and correspond to a range of energies above dissociation of 451-2950 cm(-1). The translational energy release (recoil energy) distributions are remarkably similar, peaking at very low energy (10-20 cm(-1)) and decaying in an exponential fashion to approach zero near 300 cm(-1).

Rotational distributions following van der Waals molecule dissociation: comparison between experiment and theory for benzene-Ar.

The translational energy release distribution for dissociation of benzene-Ar has been measured and, in combination with the 6(1)(0) rotational contour of the benzene product observed in emission, used to determine the rotational J,K distribution of 0(0) benzene products formed during dissociation from 6(1). Significant angular momentum is transferred to benzene on dissociation. The 0(0) rotational distribution peaks at J=31 and is skewed to low K:Javerage=27, (K)average=10.

Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states.

The potential energy surfaces of the van der Waals complexes benzene-Ar and p-difluorobenzene-Ar have been investigated at the second-order Møller-Plesset (MP2) level of theory with the aug-cc-pVDZ basis set. Calculations were performed with unconstrained geometry optimization for all stationary points. This study has been performed to elucidate the nature of a conflict between experimental results from dispersed fluorescence and velocity map imaging (VMI).