Warren Lawrance

Abstracts from the Spectra 2018 Symposium Part 2: Visualization

Publisher: MIT Press - Journals

Date: 2021

DOI: 10.1162/LEON_A_01969

Direct observation of methyl rotor and vib-rotor states of S toluene: A revised torsional barrier due to torsion-vibration coupling

Publisher: AIP Publishing

Date: 13-01-2015

DOI: 10.1063/1.4905324

Abstract: 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. The model requires that the rotor barrier height be revised from −4.84 cm−1 (methyl hydrogens in a staggered conformation) to +1.57 cm−1 (eclipsed conformation). However, the 3a2″ state lies below the 3a1″ state as expected for a staggered conformation due to energy shifts associated with the torsion-vibration coupling. It is shown that the rotor wave-functions exhibit little localization at the torsional energy minima. The variation in the m = 0 wavefunction probability distribution with torsional angle is shown to be very similar for the previously accepted negative V6 value and the torsion-vibration coupling model as this coupling shifts the phase of the wavefunction by 30° compared with its phase for V6 alone. The presence of a strong Δυ = ± 1 torsion-vibration coupling involving the lowest frequency vibrational mode provides a potential pathway for rapid intramolecular vibrational energy redistribution at higher energies.

Photodetachment velocity map imaging of the 1A′ ←2A′ transition in the AuOH anion

Publisher: Elsevier BV

Date: 04-2015

DOI: 10.1016/J.CPLETT.2015.02.053

Abstract of: Molecules as Artists—Patterns in Nature Revealed with Laser Light

Publisher: MIT Press - Journals

Date: 29-07-2021

DOI: 10.1162/LEON_A_02116

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

Publisher: AIP Publishing

Date: 28-07-2015

DOI: 10.1063/1.4927139

Abstract: We have examined the S1←S0 transition of toluene in the region from the 000 band to ∼210 cm−1 above it. The spectrum reveals methyl rotor levels of 00 toluene up to m = 6 and of the lowest frequency vibration, 201, up to m = 4. The rotor levels of both 201 and 00 are perturbed by torsion-vibration coupling. The inclusion of torsion-vibration coupling leads to the S1 torsional barrier, V6, being revised from −26.376 cm−1 to −5.59 cm−1. The torsion-vibration coupling constant is determined to be 21.1 cm−1. This situation is the S1 analogue of that recently reported for S0 toluene [Gascooke et al., J. Chem. Phys. 142, 024315 (2015)]. Torsion-vibration coupling alters both the rotor band positions and the rotational contours, which particularly affects the rotational constants associated with motion around the a-axis, about which the methyl group rotates. Every vibrational state (indicated generically by X) will be involved in the corresponding X − X201 torsion-vibration coupling so, this interaction permeates the vib-rotor manifold, providing a mechanism to enhance intramolecular vibrational energy redistribution.

Triplet lifetimes, solvent, and intramolecular capture of isoxazolones

Publisher: CSIRO Publishing

Date: 2004

DOI: 10.1071/CH03140

Abstract: The first step in the photochemical decarboxylation of isoxazolones is the formation of the triplet state of the isoxazolone. We present evidence for the first time from flash laser photolysis of the lifetime of such species, and ex les of their capture by solvent and by intramolecular cycloaddition.

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

Publisher: AIP Publishing

Date: 03-04-2012

DOI: 10.1063/1.3697474

Abstract: 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-Ar2 in the region of their S1-S0 electronic origins. The 2D-LIF spectral images reveal a number of features assigned to the van der Waals vibrations in S0 and S1. An advantage of 2D-LIF spectroscopy is that the LIF spectrum associated with a particular species may be extracted from an image. This is illustrated for fluorobenzene-Ar. The S1 van der Waals modes observed in this spectrum are consistent with previous observations using mass resolved resonance enhanced multiphoton ionisation techniques. For S0, the two bending modes previously observed using a Raman technique were observed along with three new levels. These agree exceptionally well with ab initio calculations. The Fermi resonance between the stretch and bend overtone has been analysed in both the S0 and S1 states, revealing that the coupling is stronger in S0 than in S1. For fluorobenzene-Ar2 the 2D-LIF spectral image reveals the S0 symmetric stretch van der Waals vibration to be 35.0 cm−1, closely matching the value predicted based on the fluorobenzene-Ar van der Waals stretch frequency. Rotational band contour analysis has been performed on the fluorobenzene-Ar $\\overline {0_0^0 }$000¯ transition to yield a set of S1 rotational constants A′ = 0.05871 ± 0.00014 cm−1, B′ = 0.03803 ± 0.00010 cm−1, and C′ = 0.03103 ± 0.00003 cm−1. The rotational constants imply that in the S1 00 level the Ar is on average 3.488 Å from the fluorobenzene centre of mass and displaced from it towards the centre of the ring at an angle of ∼6° to the normal. The rotational contour for fluorobenzene-Ar2 was predicted using rotational constants calculated on the basis of the fluorobenzene-Ar geometry and compared with the experimental contour. The comparison is poor which, while due in part to expected saturation effects, suggests the presence of another band lying beneath the contour.

Rate constants for the gas-phase reactions of germylene with CH3OCH3, CH3OH, CD3OD and D2O at ambient temperature

Publisher: Royal Society of Chemistry (RSC)

Date: 10-03-2003

DOI: 10.1039/B301392H

The intensity of forbidden torsional transitions in electronic spectra of molecules with a 6-fold barrier: Application to toluenes

Publisher: AIP Publishing

Date: 21-04-2014

DOI: 10.1063/1.4871008

Abstract: Franck-Condon forbidden transitions involving methyl rotor modes are seen in the S1 ← S0 spectrum of toluene and toluene-like molecules. The strongest of these rotor transitions (m″ = 1 → m′ = 2, m″ = 0 → m′ = 3a1″, and m″ = 1 → m′ = 4) have been shown by Walker et al. [J. Chem. Phys. 102, 8718 (1995)] to gain intensity through the rotor equivalent of the Herzberg-Teller mechanism. Despite the m″ = 0 → m′ = 3a2″ transition being forbidden in this formalism, it is sporadically observed. We show that this transition derives oscillator strength from incomplete mixing of the −3 and +3 free rotor basis states due to torsion-rotation coupling. Calculations demonstrate that this mechanism quantitatively explains the intensities observed for toluene, including their temperature dependence. Because the −3/+3 mixing is weakest when the torsional barrier height, V6, is small, the m″ = 0 → m′ = 3a2″ transition increases in intensity as |V6| decreases. The temperature and |V6| dependencies explain why reports of the 0 → 3a2″ transition have been intermittent. The torsion-rotation coupling mechanism is predicted to also give significant intensity to m = 0 → m = 6a2′ transitions relative to m = 0 → m = 6a1′ transitions and to provide intensity to 0 → 3a2 transitions in molecules with a 3-fold (V3) barrier. Comparison between the observed and calculated rotor band contours shows, unexpectedly, that the 3a1″ constants fail to predict the 3a2″ contour despite these two states being derived from the same free rotor basis states. Comparison with the observed spectrum also reveals differences in the separation of the S1 3a2″ and 3a1″ levels. The V6 value determined from analysis of the high resolution, rotationally resolved m″ = 0 → m′ = 3a1″ spectrum overestimates the 3a2″–3a1″ separation by 0.6 cm−1. We postulate that this may be due to torsion-vibration coupling. The observed toluene torsion-rotation contours have been modeled to provide estimates of the rotational constants for several of the torsional states.

Shear stress mediated scrolling of graphene oxide

Publisher: Elsevier BV

Date: 10-2018

DOI: 10.1016/J.CARBON.2018.05.040

Measuring the internal energy content of molecules transported across the liquid-gas interface

Publisher: IOP Publishing

Date: 09-2009

DOI: 10.1088/1742-6596/185/1/012027

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

Publisher: AIP Publishing

Date: 23-08-2004

DOI: 10.1063/1.1772355

Abstract: 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). The inconsistency is that spectra for levels of p-difluorobenzene–Ar and –Kr below the dissociation thresholds determined by VMI show bands where free p-difluorobenzene emits, suggesting that dissociation is occurring. We proposed that the bands observed in the dispersed fluorescence spectra are due to emission from states in which the rare gas atom orbits the aromatic chromophore these states are populated by intramolecular vibrational redistribution from the initially excited level [S. M. Bellm, R. J. Moulds, and W. D. Lawrance, J. Chem. Phys. 115, 10709 (2001)]. To test this proposition, stationary points have been located on both the benzene–Ar and p-difluorobenzene–Ar potential energy surfaces (PESs) to determine the barriers to this orbiting motion. Comparison with previous single point CCSD(T) calculations of the benzene–Ar PES has been used to determine the amount by which the barriers are overestimated at the MP2 level. As there is little difference in the comparable regions of the benzene–Ar and p-difluorobenzene–Ar PESs, the overestimation is expected to be similar for p-difluorobenzene–Ar. Allowing for this overestimation gives the barrier to movement of the Ar atom around the pDFB ring via the valley between the H atoms as ⩽204 cm−1 in S0 (including zero point energy). From the estimated change upon electronic excitation, the corresponding barrier in S1 is estimated to be ⩽225 cm−1. This barrier is less than the 240 cm−1 energy of 302¯, the vibrational level for which the anomalous “free p-difluorobenzene” bands were observed in dispersed fluorescence from p-difluorobenzene–Ar, supporting our hypothesis for the origin of these bands.

Rate constants for the gas-phase reactions of silylene with methanol, deuterated methanol, and water

Publisher: American Chemical Society (ACS)

Date: 16-01-2002

DOI: 10.1021/JP012773V

Fluid dynamic lateral slicing of high tensile strength carbon nanotubes

Publisher: Springer Science and Business Media LLC

Date: 11-03-2016

DOI: 10.1038/SREP22865

Abstract: 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. CNT slicing occurs with the VFD operating in both the confined mode for a finite volume of liquid and continuous flow for scalability purposes.

A “circularisation” method to repair deformations and determine the centre of velocity map images

Publisher: AIP Publishing

Date: 05-2017

DOI: 10.1063/1.4981024

Abstract: 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. While the method relies on the analysis of the structure in an image, it could also be applied to determine the “repair function” using a calibration image (or series of images) for the experiment. Once the image has been circularised it can be processed by any of the approaches that have been developed for that purpose. The analysis also enables the image centre to be determined with high accuracy. The fitting method utilises an inverse Abel transformation of the image in polar coordinates as a means to reshape the image into a series of spectral features in order to determine the radial position of features at each angle. Although the velocity distribution is not in general spherically symmetric and so this is not a mathematically correct means to extract the velocity distribution, the feature positions are accurately reproduced in the resulting spectrum while the intensity and anisotropy parameters can be remarkably close to those obtained using the proper inverse Abel transformation of the image.

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

Publisher: AIP Publishing

Date: 24-08-2012

DOI: 10.1063/1.4746688

Abstract: Sixteen intermolecular vibrational levels of the S0 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. The constants predict the observed band positions with a root mean square deviation of 0.04 cm−1. The set of vibrational levels predicted by the constants, which includes unobserved bands, has been compared with the predictions of ab initio calculations, which include all vibrational levels up to 70–75 cm−1. There are small differences in energy, particularly above 60 cm−1, however, the main differences are in the assignments and are largely due to the limitations of assigning the ab initio wavefunctions to a simple stretch, bend, or combination when the states are mixed by the cubic anharmonic coupling. The availability of these experimental data presents an opportunity to extend ab initio calculations to higher vibrational energies to provide an assessment of the accuracy of the calculated potential surface away from the minimum. The intermolecular modes of the fluorobenzene-Ar2 trimer complex have also been investigated by dispersed fluorescence. The dominant structure is a pair of bands with a ∼35 cm−1 displacement from the origin band. Based on the set of vibrational modes calculated from the fluorobenzene-Ar frequencies, they are assigned to a Fermi resonance between the symmetric stretch and symmetric short axis bend overtone. The analysis of this resonance provides a measurement of the coupling strength between the stretch and short axis bend overtone in the dimer, an interaction that is not directly observed. The coupling matrix elements determined for the fluorobenzene-Ar stretch-long axis bend overtone and stretch-short axis bend overtone couplings are remarkably similar (3.8 cm−1 cf. 3.2 cm−1). Several weak features seen in the fluorobenzene-Ar2 spectrum have also been assigned.

Relaxation of the 6 Vibrational Level in ¹B_2u Benzene by Polyatomic Colliders at Ultralow Temperatures

Publisher: American Chemical Society (ACS)

Date: 18-10-2003

DOI: 10.1021/JP030067J

Electron momentum spectroscopy of formic acid

Publisher: Elsevier BV

Date: 05-2009

DOI: 10.1016/J.CPLETT.2009.04.017

An investigation of vibration to rotation transfer in vibrational relaxation of S1 aromatics

Publisher: Elsevier BV

Date: 03-1996

DOI: 10.1016/0009-2614(96)00067-X

Electron momentum spectroscopy in the study of intermolecular interactions

Publisher: IOP Publishing

Date: 11-2008

DOI: 10.1088/1742-6596/141/1/012011

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

Publisher: AIP Publishing

Date: 28-07-2016

DOI: 10.1063/1.4959130

Abstract: 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 1.775 ± 0.005 eV and assigned to the X1Σ+←X2Σ+ transition between the anionic and neutral ground states. Franck-Condon simulations performed on density functional theory optimized geometries assisted the assignment of linear geometries to the neutral and anion and the observed vibrational progression to that of the Au–C4H stretch.

The dynamics of evaporation from a liquid surface

Publisher: Elsevier BV

Date: 09-2011

DOI: 10.1016/J.CPLETT.2011.06.010

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

Publisher: AIP Publishing

Date: 09-05-2011

DOI: 10.1063/1.3578174

Abstract: 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 technique is illustrated by application to the S1–S0 transition in fluorobenzene. Images of room temperature s les show that overlap of rotational contours by sequence band structure is minimized with 2D-LIF allowing a much larger range of rotational transitions to be observed and high precision rotational constants to be extracted. A significant advantage of 2D-LIF imaging is that the rotational contours separate into their constituent branches and these can be targeted to determine the three rotational constants in idually. The rotational constants determined are an order of magnitude more precise than those extracted from the analysis of the rotational contour and we find the previously determined values to be in error by as much as 5% [G. H. Kirby, Mol. Phys. 19, 289 (1970)10.1080/00268977000101291]. Comparison with earlier ab initio calculations of the S0 and S1 geometries [I. Pugliesi, N. M. Tonge, and M. C. R. Cockett, J. Chem. Phys. 129, 104303 (2008)10.1063/1.2970092] reveals that the CCSD/6–311G** and RI-CC2/def2-TZVPP levels of theory predict the rotational constants, and hence geometries, with comparable accuracy. Two ground state Fermi resonances were identified by the distinctive patterns that such resonances produce in the images. 2D-LIF imaging is demonstrated to be a sensitive method capable of detecting weak spectral features, particularly those that are otherwise hidden beneath stronger bands. The sensitivity is demonstrated by observation of the three isotopomers of fluorobenzene-d1 in natural abundance in an image taken for a supersonically cooled s le. The ability to separate some of the 13C isotopomers in natural abundance is also demonstrated. The equipment required to perform 2D-LIF imaging with sufficient resolution to resolve the rotational features of large polyatomics is available from commercial suppliers.

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

Publisher: AIP Publishing

Date: 07-05-2013

DOI: 10.1063/1.4803465

Abstract: Photoelectron spectra following photodetachment of the gold dicarbide anion, ${\\rm AuC}_2^ - $ AuC 2−, 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 2A′ ← 3A′ transition, involving states which we calculate to have bond angles ∼147° but with a low barrier to linearity.

Rotational Changes Accompanying Vibrational Transfer in Low-Energy Collisions between Benzene and H₂, D₂, and CH₄

Publisher: American Chemical Society (ACS)

Date: 23-10-2003

DOI: 10.1021/JP035560+

Benzene Internal Energy Distributions Following Spontaneous Evaporation from a Water−Ethanol Solution

Publisher: American Chemical Society (ACS)

Date: 19-12-2008

DOI: 10.1021/JP804270V

Discovery Projects - Grant ID: DP0453031

Start Date: 2004

End Date: 12-2008

Amount: $240,000.00

Funder: Australian Research Council

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End Date: 06-2020

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