Velocity map ion imaging

Ultrafast molecular elimination of iodine from IF2C-CF2I has been studied using the velocity map ion imaging technique in combination with femtosecond pump-probe laser excitation.51 By varying the femtosecond delay between pump and probe pulse, it has been found that elimination of molecular iodine is a concerted process, although the two carbon-iodine bonds are not broken synchronously. 

The veloeity and angular distributions of NO produced by UV photolysis of nitrosobenzene have been determined by velocity-map ion imaging. With light of A = 290.5 (S2 state) and 226 nm (5n (n > 3) states), completely isotropic velocity distributions were observed, leading to the conclusion that photodissodation occurs on a timescale much slower than rotation of the parent molecule, and after redistribution of the excess energy into the vibrational modes. 

The gas phase photodissociation of free NO2 molecules is a benchmark system which has been investigated in great detail in particular with the velocity map ion imaging technique,... 

Fig. 7.14. (a) Typical velocity map ion images of CF3 fragments escaping from helium... 

Fig. 8.2. Velocity-mapped ion image of NO7.5 scattered off of Ar at extremely high beam densities in order to suppress the build up of cold NO. The arrow indicates the laboratory origin where the cold molecules are formed, from the image one can see the velocity compression associated with the scattering from the narrowing of the scattering ring near the laboratory origin.

Crossed atomic and molecular beam (CAMB) experiments have been used for several decades to study collisional dynamics in gas phase chemistry. Combining CAMB experiments with the Velocity Mapped Ion Imaging technique, forms a powerful new tool that allows experimentalists to directly... 

The two beams intersect at 90° inside the interaction region with t3rpical vacuum pressures of 10 Torr. The beams cross between plates that form a weak uniform electric field of 200V/cm. The crossing of the molecular and atomic beams is further intersected by an ionization laser. The ionization laser(s) ionizes the molecules using resonance enhanced multi-photon ionization, REMPI. Once ionized the molecules are extracted from the interaction region by the uniform electric field into the Velocity Mapped Ion-Imaging system. 

Fig. 8.5. Velocity mapped ion image of NO colliding with Ar. The image is of NO in j = 7.5 rotational state with the velocity information coarsely indicated.

Lorenz K, Westley M, Chandler D. (2000) Rotational state-to-state differential cross sections for the HCl-Ar colhsion system using velocity-mapped ion imaging. Phys. Chem. Chem. Phys. 2 481-494. 

Wells KL, Perriam G, Stavros VG (2009) Hme-resolved velocity map ion imaging study of NH3 photodissociation. J Chem Phys 130 074308... 

The velocity mapping-ion counting technique increases the resolution of imaging data. This is clearly seen when it is compared with the data from the conventional Wiley-McLaren imaging apparatus2 or even the... 

The ion-imaging technique, introduced in 1987 by Chandler and Houston [23], has been described in full detail in several recent review articles [15,35,36]. Velocity mapping uses a different electrostatic field arrangement... 

Photochemistry of gas-phase molecules, including species of atmospheric importance the molecular photodissociation dynamics are traced by photofragment ion (velocity map) imaging. 

Figure 9.10 Exampleofion-velodtymappingofproducts in a photofragmentation experiment. Top photofragment recoil for molecular transitions with fi parallel or perpendicular to the laser field polarization E, and subsequent extraction of ionized fragments. Middle inverse Abel-transformed image of the velocity distribution of ionized D atoms produced in the photolysis of DI at A = 205 nm. Bottom angular and velodty distributions extracted from the ion image map for the D -EI and D -E I fragmentation channels. Data adapted from McDonnell and Heck J. Mass Spectrom., 1998, 33 415, with permission of John Wiley Sons Ltd...

Arthur Suits is a professor of chemistry at Wayne State University where he and his group study the many roles office radicals—atoms or molecules with unpaired electrons—in chemical processes. One of the techniques developed in his lab, DC Shce Velocity Map Imaging, uses a video camera to record images of ions formed by photo ionization after (for one example) a dissociation reaction occurs. For instance, Suits has used laser photodissociation (Section 7.4) to break deuterium bromide ( HBr or DBr) into deuterium and bromine radicals. The photodissociation occurs at a fixed photon energy... 

While velocity mapped imaging gives a direct picture of momentum space, there are some serious issues using this technique with cold molecules. The two most important are the electron recoil during the ionization step and charge repulsion from producing multiple ions per laser shot. While... 

Parker D, Eppink A. (1997) Velocity map imaging of ions and electrons using electrostatic lenses Apphcation in photoelectron and photofragment ion imaging of molecular oxygen. Rev. Sci. Instr. 68 3477-3484. 

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