High resolution slice imaging of nonadiabatic state-to-state photodynamics

Stolte, S. [Promotor]Janssen, M.H.M. [Copromotor

Slice imaging of the quantum state-to-state cross section for photodissociation of state-selected rovibrational bending states of OCS (v2=0,1,2/JlM)+hnu-->CO(J)+S(1D2)

Using hexapole quantum state-selection of OCS (v2 =0,1,2∫JlM) and high-resolution slice imaging of quantum state-selected CO (J), the state-to-state cross section OCS (v2 =0,1,2∫JlM) +h→CO (J) +S (D21) was measured for bending states up to v2 =2. The population density of the state-selected OCS (v2 =0,1,2∫JlM) in the molecular beam was obtained by resonantly enhanced multiphoton ionization of OCS and comparison with room temperature bulk gas. A strong increase of the cross section with increasing bending state is observed for CO (J) in the high J region, J=60-67. Integrating over all J states the authors find (v2 =0): (v2 =1): (v2 =2) =1.0:7.0:15.0. A quantitative comparison is made with the dependence of the transition dipole moment function on the bending angle. © 2007 American Institute of Physics

The correlation between 1(P-2(3/2))/I(P-2(1/2)) branching and CH3 rotation in photolysis of single quantum state-selected CH3I (JK=11)

The dependence of the I

RG+ formation following photolysis of NO–RG via the Ã-X̃ transition: a velocity map imaging study.

Kr+ and Xe+ formation following photodissociation of NO–RG (RG = Kr or Xe) molecules via the ÖX̃ electronic transition in the 44,150–44,350 cm−1 region has been investigated using velocity map imaging. Nuclear kinetic energy release (nKER) spectra indicate that the NO cofragment is produced in multiple vibrational states of the electronic ground state, with a high degree of rotational excitation. Photofragment angular distributions and nKERs are consistent with photo-induced charge transfer at the two-photon level followed by dissociative ionization at the three-photon level. RG+ angular distributions showing highly parallel character relative to the laser polarization axis are indicative of a high degree of molecular alignment in the dissociating species. © 2011 American Institute of Physics.</em

Slice imaging of photodissociation of spatially oriented molecules

An electrostatic ion lens to spatially orient parent molecules and to image the angular distribution of photofragments is presented. Photodissociation of laboratory-oriented molecules makes it possible to study the dynamics of the dissociation process in more detail compared to photodissociation of nonoriented molecules. Using the velocity map imaging technique in combination with the slice imaging technique, the spatial recoil distribution of the photofragments can be measured with high resolution and without symmetry restrictions. Insertion of orientation electrodes between the repeller and the extractor of a velocity mapping electrostatic lens severely distorts the ion trajectories. The position where the ions are focused by the lens, the focal length, can be very different in the directions parallel and perpendicular to the inserted orientation electrodes. The focal length depends on the exact dimensions and positions of the electrodes of the ion lens. As this dependence is different in both directions, this dependence can be used to correct for the distorted ion trajectories. We discuss the design of an electrostatic ion lens, which is able to orient parent molecules and map the velocity of the photofragments. We report sliced images of photofragments from photolysis of spatially oriented C D3 I molecules to demonstrate the experimental combination of molecular orientation and velocity map slice imaging with good resolution. © 2005 American Institute of Physics

Dynamics of the A-band ultraviolet photodissociation of methyl iodide and ethyl iodide via velocity-map imaging with 'universal' detection.

We report data from a comprehensive investigation into the photodissociation dynamics of methyl iodide and ethyl iodide at several wavelengths in the range 236-266 nm, within their respective A-bands. The use of non-resonant single-photon ionization at 118.2 nm allows detection and velocity-map imaging of all fragments, regardless of their vibrotational or electronic state. The resulting photofragment kinetic energy and angular distributions and the quantum yields of ground-state and spin-orbit excited iodine fragments are in good agreement with previous studies employing state-selective detection via REMPI. The data are readily rationalised in terms of three competing dissociation mechanisms. The dominant excitation at all wavelengths studied is via a parallel transition to the (3)Q0 state, which either dissociates directly to give an alkyl radical partnered by spin-orbit excited iodine, or undergoes radiationless transfer to the (1)Q1 potential surface, where it dissociates to an alkyl radical partnered by iodine in its electronic ground state. Ground state iodine atoms can also be formed by direct dissociation from the (1)Q1 or (3)Q1 excited states following perpendicular excitation at the shorter and longer wavelength region, respectively, in the current range of interest. The extent of internal excitation of the alkyl fragment varies with dissociation mechanism, and is considerably higher for ethyl fragments from ethyl iodide photolysis than for methyl fragments from methyl iodide photolysis. We discuss the relative advantages and disadvantages of single-photon vacuum-ultraviolet ionization relative to the more widely used REMPI detection schemes, and conclude, in agreement with others, that single-photon ionization is a viable detection method for photofragment imaging studies, particularly when studying large molecules possessing multiple fragmentation channels

Multimass velocity-map imaging with the Pixel Imaging Mass Spectrometry (PImMS) sensor: an ultra-fast event-triggered camera for particle imaging.

We present the first multimass velocity-map imaging data acquired using a new ultrafast camera designed for time-resolved particle imaging. The PImMS (Pixel Imaging Mass Spectrometry) sensor allows particle events to be imaged with time resolution as high as 25 ns over data acquisition times of more than 100 μs. In photofragment imaging studies, this allows velocity-map images to be acquired for multiple fragment masses on each time-of-flight cycle. We describe the sensor architecture and present bench-testing data and multimass velocity-map images for photofragments formed in the UV photolysis of two test molecules: Br(2) and N,N-dimethylformamide

PImMS: A self-triggered, 25ns resolution Monolithic CMOS Sensor for Time-of-Flight and Imaging Mass Spectrometry

In this paper, we present the Pixel Imaging Mass Spectrometry (PImMS) sensor, a pixelated Time-of-Flight (TOF) sensor for use in mass spectrometry. The device detects any event which produces a signal above a programmable threshold with a timing resolution of 25ns. Both analogue and digital readout modes are available and all pixels can be individually trimmed to improve noise performance. The pixels themselves contain analogue signal conditioning circuitry as well as complex logic totalling more than 600 transistors. This large number can be achieved without any loss of quantum efficiency thanks to the use of the patented Isolated N-well Monolithic Active Pixels (INMAPS) process. In this paper, we examine the design of the PImMS 1.0 device and its successor PImMS 2.0, a significantly enlarged sensor with several added features. We will also present some initial results from mass spectrometry experiments performed with PImMS 1.0. © 2012 IEEE

State-resolved diffraction oscillations imaged for inelastic collisions of no radicals with he, ne and ar

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