Velocity map imaging of the photodissociation of CF3I+ in the Ã←X̃ band

Abstract

The photodissociation dynamics of CF 3 I ϩ has been investigated within the à ←X band by means of velocity map ion imaging. The CF 3 I ϩ cation is prepared by resonance-enhanced multiphoton ionization of CF 3 I via the ͓X 2 E 3/2 ͔6 p, ͓2͔5 0 1 band, and the (X 2 E 3/2) ground-state population in the CF 3 I ϩ ion is unambiguously characterized by using photoelectron spectroscopy. Photodissociation of the state-selected CF 3 I ϩ ion results in fragmentation to both CF 3 ϩ ϩI and CF 3 ϩI ϩ. The translational energy distribution derived from the two-dimensional images of the CF 3 ϩ fragments shows vibrational progressions that provide detailed information on the channeling of the parent internal energy into the dissociation process. The translational energy distribution of the CF 3 ϩ fragment shows a one-to-one dependence on the excitation energy, which is typical of a single-photon dissociation process. The observation of a repeated pattern of rings in the CF 3 ϩ images with an interval of ϳ800 cm Ϫ1 indicates that the 2 umbrella mode of the CF 3 ϩ fragment is excited upon dissociation. The low-kinetic-energy release observed in this channel indicates that substantial energy is deposited into the internal degrees of freedom of the CF 3 ϩ fragment and suggests that the dissociation is controlled by the Franck-Condon factors between the parent ion and fragments. The translational energy distribution of the I ϩ fragment is independent of the excitation wavelength and includes a feature peaking at near-zero kinetic energy. Plausible mechanisms for the CF 3 ϩ and I ϩ dissociation channels are discussed in terms of the observed kinetic energy and anisotropy distributions derived from the two-dimensional ion images.

Neutral photodissociation of superexcited states of molecular iodine

“…Of course, this spectroscopy requires tunable laser light, though not necessarily in the vacuum ultraviolet. For example, in a molecule such as CF 3 I, recently studied by Aguirre and Pratt 38,39 and by Waits et al, 40 the ionization potential of CF 3 I is 10.3716 eV, and the dissociation energies for CF 3 I + to CF 3 + +I͑ 2 P 3/2 ͒ or CF 3 +I + ͑ 3 P 2 ͒ are 1.012 and 2.41 eV, respectively. Thus, dissociative ionization to CF 3 + is possible above 11.384 eV ͑or three photons at wavelengths below 326 nm͒, whereas dissociative ionization to I + is possible above 12.782 eV ͑or three photons at wavelengths below 291 nm͒.…”

The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

“…61,62 Aguirre and Pratt studied the twophoton resonant, three-photon ionization spectrum of CF 3 I using velocity map imaging. 59,60 Two photon absorption in the wavelength interval ranging from 294 to 304 nm excites the parent molecule to a low energy Rydberg state, where it absorbs a third photon to reach the ionic ground state ͑X 2 E 3/2 ͒. After the three photon absorption, the CF 3 I + ion does not possess enough internal energy to dissociate and require absorption of an additional photon to decompose into CH 3 + ͑ ͒ and I͑ 2 P J/2 ͒ fragments.…”

Photoelectron photoion coincidence imaging of ultrafast control in multichannel molecular dynamics

“…The ionization of CF 3 I in the nanosecond regime via multiphoton absorption is usually realized through higher lying Rydberg states which serve as resonant intermediate levels. [42][43][44]50 The spectroscopy of the ionized CF 3 I + cation was investigated by Aguirre and Pratt 50,56 in the spectral range around 300 nm using two-photon resonant, three-photon ionization to prepare the ground state CF 3 I + , followed by the absorption of an additional (forth) photon leading to fragmentation of the parent ion. Recently, such fragmentation dynamics in CF 3 I + , due to further absorption of the parent ion, was also studied using the novel Amsterdam coincidence photoelectron-photoion imaging apparatus.…”