Imaging Polyatomic Molecules in Three Dimensions Using Molecular Frame Photoelectron Angular Distributions (original) (raw)
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Journal of Physics B: Atomic, Molecular and Optical Physics, 2012
We present experimental measurements and theoretical calculations for the photoionization of CH 4 at the carbon K-edge. Measurements performed using cold target recoil ion momentum spectroscopy (COLTRIMS) combined with complex Kohn variational calculations of the photoelectron in the molecular frame demonstrate the surprising result that the low energy photoelectrons effectively image the molecule by emerging along the bond axes. Furthermore, we observe a dynamic breakdown of axial recoil behaviour in one of the dissociation pathways of the intermediate dication, which we interpret using electronic structure calculations.
Photoelectron angular distributions from strong-field ionization of oriented molecules
Nature Physics, 2010
The combination of photoelectron spectroscopy and ultrafast light sources is on track to set new standards for detailed interrogation of dynamics and reactivity of molecules . A crucial prerequisite for further progress is the ability to not only detect the electron kinetic energy, as done in traditional photoelectron spectroscopy, but also the photoelectron angular distributions (PADs) in the molecular frame . Until recently the only method relied on determining the orientation of the molecular frame after ionization .
Imaging molecular isomerization using molecular-frame photoelectron angular distributions
Journal of Physics B: Atomic, Molecular and Optical Physics, 2012
We report the results of an ab initio theoretical study of K-shell photoionization of the monocation of acetylene in its ground (X) and electronically excited (A) states using the complex Kohn variational method. We show how the molecular-frame photoelectron angular distributions (MFPADs), which are sensitive to the instantaneous positions of the nuclei, can be used to monitor the isomerization of the excited cation from an initial linear geometry to a final vinylidene-like structure.
Imaging of Oriented Molecules †
The Journal of Physical Chemistry A, 1997
Hexapole state selection and orientation of parent molecules is combined with two-dimensional ion imaging of photofragments to study the direct photolysis of deuterated methyl iodide molecules (CD 3 I) at 266 nm. The combination of these two techniques allows us to create an essentially single quantum state-selected beam of oriented molecules, which are subsequently photodissociated, and to measure the final state-, velocity-, and angle-resolved recoil distribution of the photofragments. Extensive measurements have been done on the variation of the recoil distribution with the orientation field strength applied. These measurements allow a quantitative comparison of the orientation distribution of state-selected methyl iodide molecules with theoretical Stark effect calculations. For the prompt dissociation of CD 3 I at 266 nm the angular recoil distribution of the I( 2 P 1/2 ) photofragment reflects predominantly the initial spatial orientation of the stateselected parent. A comparison is presented between the fragment recoil distributions when different initial oriented parent states are selected. ‡ E-mail address: mhmj@chem.vu.nl. † Dedicated to the late Prof. R. B. Bernstein who initiated the attempts of measuring the orientation of molecules via a prompt photodissociation along the molecular axis.
Physical Review A
We probe the time-dependent ionization dynamics of impulsively excited rotational wave packets of N 2 , CO 2 , and C 2 H 4 using broadband ultraviolet pulses centered at 262 nm. Photoelectron momentum distributions recorded by velocity-map imaging show a strong dependence on alignment, on multiphoton order, and on the electronic and vibrational states of the cation. We show that substantial information about the molecular-frame photoelectron angular distribution can be obtained from the high-order laboratory-frame asymmetry parameters without any prior knowledge of the photoionization process. We also compare few-photon ionization with one-photon ionization and strong-field ionization.
Dependence of strong-field photoelectron angular distributions on molecular orientation
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
We have analysed angular distributions of the photoelectron yields arising from strong-field ionization of diatomic and polyatomic linear molecules using a leading-order intense-field S-matrix theory. For molecules with active π electrons the distribution is found to strongly depend on the degree of molecular alignment, showing a nodal minimum along the laser polarization direction as a characteristic signature.
Physical Review A, 2013
Photo-excitation of neutral ethylene to its V state initiates conformational changes of the molecule through a complex potential energy surface, characterized by the presence of several conical intersections. Eventually, the migration of one hydrogen atom to another carbon site occurs via a non-adiabatic passage and leads to the formation of the stable and asymmetric ethylidene isomer. With the recent advance in ultra fast x-ray laser pulses, it is now possible to image such photoisomerization processes by resolving the geometrical change of a molecule in the time-scale of a reaction. One suggested technique consists on collecting photoelectron and measuring their angular distribution in the fixed-body frame via momentum imaging techniques on fast charged fragments produced from a Coulomb explosion. In order to estimate the interest of this experimental technique, we have calculated carbon K-shell molecular-frame photoelectron angular distributions (MFPADs) at a few relevant geometries in the isomerization of ethylene. Moreover, the obtained theoretical results are compared with available experimental data at the ground state geometry of ethylene and a very good agreement is observed. Our results indicate that, in spite of the complexity of this system and the presence of two heavy atomic centers, the main features of the photoisomerization of ethylene can be traced from the shape of the MFPADs.
Chemical Physics Letters, 2003
We present explicit expressions for the molecular frame and laboratory frame photofragment angular distributions from oriented parent molecules, in terms of the dynamically significant molecular frame angles between the recoil direction and the transition and permanent dipole moments of the molecule. We discuss how these angles can be measured from distinct experimental geometries. Explicit examples are given on the extracted information of the molecular frame photodissociation, especially in case of non-axial recoil dynamics.