SDG2011 Posters

The full list of poster presentations is listed below. The list was last updated on 20/12/10

Please note that posters should be in portrait format (with a maximum size of A0)

1. A new method of performing pump-probe spectroscopy using Hadamard transforms

A new method of performing flash-photolysis or pump-probe experiments is proposed and demonstrated. Instead of using a continuous beam to monitor changes caused by the pump pulse, the probe’s intensity is encoded ‘on’ and ‘off’ in a pattern based on a Hadamard sequence. The total intensity of the probe is measured after every excitation event and recorded. The experiment is then repeated with the probe sequence rotated by one step in the sequence until the original sequence is again produced. To produce the transient signal the vector containing all the integrated probe signals is transformed using a matrix based on the pattern encoded onto the probe. This method removes the need for fast detecting equipment as the time resolution is determined by the on-off pulse duration of the probe.

Because of a great variety of applications there has been considerable research effort devoted to the design of molecules having strong two-photon absorption response. Here it is described how advanced computation of this non-linear optical process is able to contribute by detailing molecular features that allow one to tune molecules to have desired properties.

3. Superfluid helium droplets: A new tool for the synthesis of core-shell nanoparticles

To date, the focus of work around the world using helium nanodroplets has been on the study of small molecules and clusters. However, the unique properties of superfluid helium droplets offer new possibilities beyond the traditional Physical Chemistry community, e.g., synthesis of novel core-shell nanoparticles by adding dopants to helium droplets one by one. In particular the sequential addition of pick-up material provides a potential route to core-shell nanoparticles with almost limitless variety of compositions. Thus it is now possible to conceive of novel core-shell combinations which cannot be realised by any conventional ‘wet’ chemical route, and this is to be explored in our new research programme.

4. Symmetry-related ⁵⁷Fe Mössbauer microscopic electric-field-gradient tensors

When a Mössbauer-active ⁵⁷Fe nucleus embedded in a single crystal has lower point symmetry than the host unit cell, several symmetry-related microscopic sites can contribute spectral intensity to the same macroscopic quadrupole doublet. Methodology has been developed assuming anisotropic Lamb-Mössbauer factors, and experiments performed on two prototypical ferrous high-spin species in order to resolve microscopic contributions.

5. Femtosecond studies of molecular fragmentation in a linear ion trap: A platform for biomolecular mass spectrometry

C. R. Calvert, O. Kelly, M. J. Duffy, L. Belshaw, R. B. King and J. B. Greenwood

Intense femtosecond laser pulses provide powerful, tunable tools for ionisation and fragmentation studies of molecular targets. Using such pulses in combination with our linear electrostatic ion trap, KEIRA, we introduce a novel method for high-resolution mass spectrometry. By coupling this technique to schemes for creating biomolecules in the gas-phase, we create a platform for future studies of biomolecular fragmentation dynamics.

The excited states of protonated gas phase tryptophan will be explored using time resolved hydrogen imaging. TrpH⁺ is introduced into the gas phase using electrospray ionisation. A hydrogen atom is then dissociated by a 200 nm laser pulse. The hydrogen is probed using (2+1) REMPI and velocity map imaging to yield the dissociation energy and anisotropy. These data will help illuminate the πσ* state in Trp, which is thought to be key to its high resistance to photo damage in biological systems.

Intramolecular vibrational redistribution (IVR) has been investigated using picosecond time-resolved photoelectron spectroscopy. IVR involves the radiationless transfer of energy from an initially excited bright vibrational state into optically forbidden dark states. When only a few states are coupled, IVR can be observed as quantum beating patterns in the time domain. Results for parafluorotoluene will be presented at the meeting.

Ionisation of small molecules is an important process in many environments, such as plasmas and planetary atmospheres. Accurate models of these environments require reliable data on the formation efficiency of any ions created following ionisation. Using a time-of-flight mass spectrometer coupled with a 2D coincidence technique we can measure for the first time precursor specific partial ionisation cross sections. In addition, investigation of our coincidence spectra allow us to determine the kinetic energy releases of dication dissociations, and hence probe the electronic state energies of dications.

M. Duffy, C. R. Calvert, O. Kelly, R. B. King, L. Belshaw, I. D. Williams and J. B. Greenwood

Studies of the ionisation and fragmentation of allene (C₃H₄) been performed with intense femtosecond laser pulses. Ionic fragments are analysed in a linear electrostatic ion trap that acts as a high resolution mass spectrometer. Variation of pulse parameters, such as duration and peak intensity, are found to dramatically influence the fragmentation pattern.

FTMS of tert-butyl acetate in the region 5.5-16.5 GHz is reported. Using optimisation calculations the A and E states of the lower energy rotamer were analysed, the rotational constants for each state, the centrifugal constants, the constants for the internal motion and the barrier height to rotation were also determined.

11. Nanosecond-timescale UV multiphoton ionization (MPI) processes in nucleic acid bases and their hydrates

MPI mass spectra of hydrated uracil clusters will be presented for the first time. Cluster ion distributions and laser fluence dependences will be compared for different mixed complexes of adenine, thymine, uracil, and water molecules. Interpretations relating to electronic excited state lifetimes, relaxation mechanisms, and photo-induced chemistry will be discussed.

Oscillatory structures within the parity conserving, fully lambda-doublet resolved differential cross-sections (DCSs) for the collisions of NO(X)+Ar are shown to arise via interference between trajectories impacting upon the either the flatter middle or the pointed ends of the NO molecule.

13. Interaction of hydrogen Rydberg molecules with a silicon semiconductor surface

The present research work focuses on the interaction of H₂ Rydberg molecule with doped silicon semiconductor surfaces. Para H₂ Rydberg states with principal quantum number n = 17 - 21 and core rotational quantum number N⁺ = 2 are populated via resonant two photon VUV - UV excitation. The nature of dopant atoms in the silicon wafer is seen to affect the ionization process in different ways: For lower principal quantum number Rydberg states, p - type dopants are seen to enhance the detection of ions, while as n - type dopants diminish ion detection. The surface ionisation profiles diminished with increasing dopant concentration as a consequence of complete electric shielding and the p - type Si surface has higher ion detectability than the n - type doped Si surface due to the positive surface charge surrounding the dopant atoms.

14. A trajectory study of chlorine reactions using a multi-purpose specific reaction parameter method

S. J. Greaves, R. A. Rose, F. Abou-Chahine, D. R. Glowacki, D. Troya and A. J. Orr-Ewing

A specific reaction parameter (SRP) Hamiltonian previously developed for the Cl + ethane reaction is found to describe the potential energy surface of the related Cl + methane reaction, opening the possibility for SRPs being used to describe families of reactions, e.g. Cl + alkane reactions.

The design and assembly of an infra-red spectrometer coupled to a boxcar integrator, to record femtosecond transient absorption spectra of photovoltaic materials for the fabrication and optimization of an all-carbon heterojunction solar cell, is presented. The componentry, development of the software to drive the system and acquire data, and general progress are reported.

Here we report on an initial attempt to record the first electronic spectra of Ca(NH₃)_n clusters. This builds upon previous work in our laboratory focusing on alkali-ammonia clusters, both using vibrational and electronic spectroscopy. However, although Ca(NH₃)_n clusters are made in these experiments, as shown by mass spectrometry, no spectra have been successfully recorded by our photodepletion technique. However, Ca(NH₃)_nH₂ clusters are also formed under our experimental conditions and this cluster does show a depletion spectrum in the infrared. This spectrum is presented here along with the results of some supporting calculations

17. Time resolved velocity map imaging of methyl radical elimination from anisole

To date H-atom elimination from small heteroaromatics has been the primary study of ps* mediated photodissociation in such species. Here we present, to the best of our knowledge, the first time and energy resolved study of methyl detachment from heteroaromatic systems. The results show a competition between an ultrafast process and a statistical component.

Infrared multiplephoton dissociation spectroscopy in the range 100 to 2000 cm^-1 is used to probe the structures of small platinum clusters and their complexes with atoms and molecules (H, H₂ and CH₄) with the aim of elucidating the size and structure dependence of the elementary reactions occurring during complex formation.

Three fluorinated ethenes, monofluoroethene, 1,1-difluoroethene and trifluoroethene were studied using the resident imaging photoelectron photoion coincidence iPEPICO apparatus at the X04DB beamline, the Swiss Light Source, in an attempt to gain insight into their complex dissociation dynamics.

20. Quantum-chemical study and FTIR jet spectroscopy of CHCl₃–NH₃ association in the gas phase

High level ab initio quantum chemical calculations have been performed on the association of chloroform with ammonia in the gas phase and compared to direct absorption infrared spectra at very low temperatures.

Cavity ring-down spectroscopy is a highly sensitive analytical technique commonly used to measure absorptions of trace gases. Using a loop of optical fibre as the cavity allows for the analysis of picolitre liquid samples, with applications in lab-on-a-chip technology including reaction monitoring and environmental sensing.

22. Measuring molecular dynamics in solution with ultrafast 2D-IR spectroscopy

We report on the development of collinear Fourier Transform 2D-IR spectroscopy and make comparisons with frequency domain techniques. Applications of 2D-IR methods to investigate fluxional dynamics of Fe₃(CO)₁₂ in solution and vibrational coupling of CO and CN ligands in hydrogenase enzyme model compounds are also described.

24. The NO(X ²P)-Kr complex: A combined microwave spectroscopy and quantum study

The lower bound states of the krypton-nitric oxide (Kr-NO) open-shell van der Waals complex have been studied using Fourier Transform Microwave Spectroscopy (FTMS) and bound calculations based on a recent coupled-cluster [CCSD(T)] ab initio potential energy surface (PES).

25. The scalar and vector correlations of molecular collisions using frequency modulated spectroscopy

Frequency modulated spectroscopy (FMS) is employed to investigate the post-collisional behaviour of state-selected CN(A²P) and help reveal the underlying scalar and vector correlations by means of rotational energy transfer (RET), elastic depolarization and polarization transfer studies. Such measurements are sought after with reference to recent experimental and theoretical advances on the collisional evolution of related open-shell species.

26. The detection of trace concentrations of helium and argon in gas mixtures by laser-induced breakdown spectroscopy

This poster will describe the first demonstration of the detection of trace concentrations of helium and argon in binary and ternary gas mixtures with nitrogen by laser-induced breakdown spectroscopy. Analytical data will be rpresented.

27. High resolution photoelectron spectra and non-cylindrically symmetric photoelectron angular distributions from velocity map images

Slow Electron Velocity Imaging (SEVI) is a variant of Velocity Map Imaging (VMI) in which a two colour ionization scheme is used in order to achieve a significantly improved resolution. Photoelectron spectra of para-fluorotoluene (PFT) have been measured with typical linewidths of ~ 5 cm^-1. Non-cylindrically symmetric photoelectron angular distributions are found using a tomographical reconstruction technique.

28. Development of a new photoelectron spectroscopy instrument combining an electrospray ion source and photoelectron imaging

A new apparatus has been constructed that combines electrospray ionisation with a quadrupole mass-filter, hexapole ion-trap and velocity-map imaging. The purpose is to record photoelectron images of isolated chromophore anions. To demonstrate the capability of our instrument we have recorded the photodetachment spectra of isolated deprotonated phenol and indole anions. To our knowledge, this is the first time that the photodetachment energy of the deprotonated indole anion has been recorded.

Sulphur tetrafluoride is a stable radical and an important component of technological plasmas whose behaviour upon photoionisation is almost completely unstudied. This poster reports an initial study of the double ionisation of sulphur tetrafluoride in the 30 - 100 eV photon range.

30. Progress towards studying low temperature chemical collisions with state-selected neutral molecules and ion Coulomb crystals

L. Pollum, L. Harper, K. S. Twyman, J. M. Oldham, A. D. Gingell, M. T. Bell and T. P. Softley

We report progress towards studying ion-molecule reactions using trapped laser-cooled ions in combination with two different sources of cold neutral molecules. A Stark decelerator beamline is used to produce tunable-energy packets of quantum state selected cold polar molecules which are focussed into the ion trap. In another experiment, helium buffer gas at 4 K is used to prepare cold effusive molecular beams to load an electrostatic velocity selector.

The velocity map imaging technique will be used to yield images of fragments resulting from the photodissociation of surfaces. Specifically we are using fluorinated self-assembled-monolayers due to their well defined structure and ability to act as models for (in this case fluorinated) polymer systems.

C. J. Rennick, J. Ortega-Arroyo, P. Godin, L. Fu, N. Saquet, J. P. Morrison and E. R. Grant

We excite nitric oxide entrained in a molecular to high Rydberg states lying below the lowest ionization limit. This dense collection of molecules ionize spontaneously, forming a plasma of NO⁺ ions and free electrons trapped by the potential well formed by a small excess of positive charge. The plasma travels with the velocity of the molecular beam through the field-free region of an electron spectrometer for a variable distance before detection. In this way we can gauge the expansion and decay of the plasma as a function of time. The expansion rate is well represented by a plasma model with an electron temperature of 5 K. Decay of the plasma can occur by dissociative recombination of NO⁺ cations and electrons, and electron evaporation. The recombination rate is second-order in electron density, with a rate coefficient that lies close to the theoretical value for nitric oxide dissociative recombination at our electron temperature.

Time resolved Fourier Transform Infrared (FTIR) emission spectroscopy has been employed in the study of collisional quenching of electronically excited A²S⁺ state of nitric oxide, revealing the nascent product state vibrational distribution. A range of collision partners were studied, and show that the quenching mechanism is strongly collision partner dependent, proceeding in some cases via collisional dissociation of the quencher.

34. H-atom elimination via ps* states in N-containing heterocyclic aromatics

The related N-atom containing aromatics pyrrole, imidazole, and pyrazole play a vital role as fundamental molecular units in numerous biological systems, such as amino acids and DNA bases. Here we specifically focus on pyrazole and present evidence for ultrafast H-atom elimination following photoexcitation at 200 nm (6.2 eV), via the repulsive ps* state along the N-H bond co-ordinate, using femtosecond time-resolved velocity map ion imaging.

A. M. Roland, A. Trottier, D. Carty, W. Doherty, M. Bell, T. P. Softley and E. Wrede

The photostop technique uses photodissociation to produce cold atomic or molecular fragments from precursor molecules seeded in a molecular beam. Results are presented for the production of cold NO from NO₂, and Br from Br₂. Current development of the experiment is discussed.

We report measurements of self- and nitrogen- pressure broadening of the P(11) line in the v₁ + v₃ combination band of acetylene at 195 739.649 513(8) GHz by absorption of radiation emitted by an extended cavity diode laser referenced to a femtosecond frequency comb. Broadening, shift and narrowing parameters were determined at 296 K. In units of cm^-1/atm., we find 0.156283(60), -0.011719(59) and 0.0527(14) for the acetylene self-broadening, shift and narrowing, and 0.0951716(87), -0.0092639(48) and 0.03057(45), respectively for the nitrogen gas parameters. The uncertainties are expressed as one standard deviation (in parenthesis) in units of the last digit reported. These parameters are 2-3 orders of magnitude more precise than those reported in previous measurements.

37. Bimolecular reactions in helium droplets activated by the charge transfer process

Helium droplets have been used to form molecular ions by charge transfer ionization of molecular species. The electron impact ionization of a doped helium droplet initially produces He⁺ ions which subsequently transfer their charge to a dopant molecule. In this study N₂, H₂, CO and O₂ were co-embedded inside the droplet. We have found that charge transfer from He⁺ can lead to chemical reactions between two dopant molecules and form molecular ions. From a combination of the listed diatomic molecules, important atmospheric species, such as NH3⁺, CO₂⁺ and NO_x⁺ (x = 1, 2) have been observed in the form of ionic products.

When close to a metal surface (~4n²) the weakly bound electron of a Rydberg state can be transferred into the conduction band of the metal. In this poster, we present some recent experimental results of the charge transfer of Rydberg hydrogen atoms with a gold surface. The effects of Rydberg orbital size, collisional velocities, and polarisation with respect to the surface on the ionisation dynamics are investigated. Classical and quantum wave-packet calculations modelling these ionisation behaviours are also presented.

39. Investigating the excited electronic states of BaOH via laser spectroscopy and ab initio calculation

Two bands for the A'-X transitions of BaOH and BaOD have been rotationally analyzed using high-resolution V-type optical-optical double resonance spectroscopy. Measured rotational lines have been assigned and rotational and fine structure parameters determined through a combined least-squares fit with the millimeter-wave pure rotational data of the X state. Ab initio calculations have been carried out to further understand the nature of the BaOH excited states. The D', D, C, B, A, A' and X states have been optimised with a state averaged calculation using the MolPro software. Calculated vertical term energies show relatively good agreement with existing optical data.

40. Construction of a miniature crossed-molecular beam machine to image inelastic and reactive scattering

Insight into construction of a miniature crossed-molecular beam machine with velocity map imaging detection will be presented. This instrument provides an improved capability to study bimolecular scattering with high kinetic energy resolution. One of the reactions that will be studied in future is Cl with neopentane (C₅H₁₂); therefore, a preliminary ab-initio calculation of this reaction will be presented.

41. High-resolution thermochemistry of fragment cations of fluorinated and chlorinated methane molecules: Results from the imaging PEPICO apparatus at the Swiss Light Source

We have recorded the first and second fragment ions, corresponding to cleavage of the weakest and second-weakest bonds, following VUV photodissociative ionisation of five halogenated methane molecules: CH₃Cl, CH₂Cl₂, CHCl₃, CH₃F and CH₂F₂. Measurements are made at the VUV beamline of the Swiss Light Source in the range 10-15 eV with a resolution approaching 0.001 eV (or 8 cm^-1). From an accurate determination of the energy at which the parent ion disappears completely, we determine the enthalpy of the corresponding unimolecular reaction at 0 K, and hence the 0 K enthalpy of formation of the fragment cation. In principle, this technique allows the determination of enthalpies of formation of radical cations to an accuracy approaching 0.1 kJ mol^‑1.

N. Walker, V. A. Mikhailov, F. J. Roberts, S. L. Stephens, S. J. Harris, D. P. Tew, J. N. Harvey and A. C. Legon

Pure rotational spectra of H₂O-CuCl and H₂O-AgCl have been measured and analysed to determine precise structural parameters. In each case, the heavy atoms are collinear while the local C₂ axis of the water molecule intersects the axis defined by the heavy atoms to define an angle. Each molecule undergoes rapid inversion between two equivalent structures where this angle has equal magnitude but opposite sign.

Changes in electronic structure can trigger chemical processes. A simple example is dissociative electron attachment, where the attachment of an electron causes bond dissociation and fragmentation. More subtle processes are possible, though. An area of particular practical interest is the initiation of proton transfer across a hydrogen bond by the movement of an electron in a system. This proton-coupled electron transfer (PCET) is important in charge transfer and catalysis. Tautomerisations driven by electron binding have a particular practical importance in the interactions of nucleic acid bases with additional electrons. In this poster we summarise some of our recent research into proton transfer in the hydrogen-bonded NH₃HX system (X=halogen) triggered by the weak binding and consequent stabilisation of an extra electron by the system’s dipole. This includes material published as Eustis et al., Science, (2008), 319, 936; and Eustis et al., J. Phys. Chem. A, (2010), 114, 1357.

44. Improved detection sensitivity with cavity enhanced laser induced fluorescence

This poster accompanies the talk from Scott Sanders on Cavity Enhanced Laser Induced Fluorescence providing further details on the technique and its applications. By combining Cavity Ring Down Spectroscopy and Laser Induced Fluorescence a new cavity based technique has been created with the potential to overcome the shortcomings of each and improve detection sensitivity overall.

45. State-selective preparation of translationally cold molecular ions in ion traps

We present a new method for the generation of rotationally and vibrationally state-selected, translationally cold molecular ions in ion traps. Our technique is based on the state-selective threshold photoionization of neutral molecules followed by sympathetic cooling of the resulting ions with laser-cooled calcium ions. Using N₂⁺ ions as a test system, we achieve > 90 % selectivity in the preparation of the ground rovibrational level and state lifetimes on the order of 15 minutes limited by collisions with background- gas molecules. Our approach opens up new perspectives for cold quantum-controlled ion-molecule-collision studies, frequency-metrology experiments with state-selected molecular ions and molecular-ion qubits.

We present progress towards imaging mass spectrometry. Using a standard velocity map imaging set-up we have recorded mass spectra concurrent with dynamical data at multiple time delays after each laser shot. We present and discuss data collected using a framing camera and an intelligent pixel detector, and describe a purpose-built detector, currently under characterisation, that promises a large advance in recording the complete (x,y,t) data volume available.

47. Novel applications in ion imaging technologies

B. Winter, C. Slater, M. Brouard, E. Campbell, E. Halford, A. Johnsen, S. Lucas, A. Nomerotski, C. Vallance and W.-H. Yuen

Novel experiments in ion imaging have recently been made possible through the introduction of fast imaging devices. Proof-of-concept experiments in the areas of imaging mass spectrometry (IMS) and photoelectron-photoion coincidence (PEPICO) are presented. Furthermore, initial results from a comprehensive study of the photodissociation of Cl₂, with a view to measuring the electronic angular momentum polarisation of the resultant atomic photofragments are included.