High-resolution Rydberg tagging time-of-flight measurements of atomic photofragments by single-photon vacuum ultraviolet laser excitation

Abstract

By coupling a comprehensive tunable vacuum ultraviolet (VUV) laser system to a velocity-mapped ion imaging apparatus, we show that high-resolution high-n Rydberg tagging time-of-flight (TOF) measurements of nascent atomic photofragments formed by laser photodissociation can be made using single-photon VUV laser photoexcitation. To illustrate this single-photon Rydberg tagging TOF method, we present here the results of the VUV laser high-n Rydberg tagging TOF measurements of O((3)P(2)) and S((3)P(2)) formed in the photodissociation of SO(2) and CS(2) at 193.3 and 202.3 nm, respectively. These results are compared to those obtained by employing the VUV laser photoionization time-sliced velocity-mapped ion imaging technique. The fact that the kinetic energy resolutions achieved in the VUV laser high-n Rydberg tagging TOF measurements of O and S atoms are found to be higher than those observed in the VUV laser photoionization, time-sliced velocity-mapped ion imaging studies show that the single-photon VUV laser high-n Rydberg tagging TOF method is useful and complementary to state-of-the-art time-sliced velocity-mapped ion imaging measurements of heavier atomic photofragments, such as O and S atoms. Furthermore, the general agreement observed between the VUV laser high-n Rydberg tagging TOF and velocity-mapped ion imaging experiments supports the conclusion that the lifetimes of the tagged Rydberg states of O and S atoms are sufficiently long to allow the reliable determination of state-resolved UV photodissociation cross sections of SO(2) and CS(2) by using the VUV laser high-n Rydberg tagging TOF method.

Branching Ratios of the N(2D03/2) and N(2D05/2) Spin–Orbit States Produced in the State-Selected Photodissociation of N2 Determined Using Time-Sliced Velocity-Mapped-Imaging Photoionization Mass Spectrometry (TS-VMI-PI-MS)

“…The TS-VMI-PI-MS apparatus used in the present study is essentially the same as the one used in the former studies and a detailed description has been previously published. , Smaller apertures were placed between the photoexcitation/photoionization (PEX/PI) chamber and the four-wave mixing chambers used to produce the two tunable VUV lasers. These apertures minimize the amount of Xe or Kr used for the four-wave mixing that enters the interaction region.…”

“…These experiments are performed in the interaction region of a differential pumped time-sliced velocity-mapped-imaging photoionization (TS-VMI-PI) apparatus that allows the VUV radiation to pass from the four-wave-mixing chamber into it without encountering any windows or mirrors. In this interaction region the VUV laser beam that has a spectral bandwidth ∼0.4 cm –1 encounters a pulse of N 2 molecules that have been cooled to a nitrogen population consisting of mostly N 2 (X 1 Σ g + , v″ = 0, J″=0 or 1) in the supersonic expansion of the molecular beam. , This apparatus has been used to study all the excited states of N 2 that can be directly excited by radiation from N 2 (X 1 Σ g + , v″ = 0, J″ = 0 or 1) in the energy range from 100 808 to 122 159 cm –1 . Two tunable VUV laser beams were employed in these studies.…”

Laser ionisation detection of O(3Pj) atoms in the VUV; application to photodissociation of O2

“…It is, for instance, possible to detect laser-induced fluorescence after this excitation step [10]. Another method uses a second laser with a wavelength of 305 nm to excite the intermediate 3s state to high-lying Rydberg states which are then field ionised in a time-of-flight Oatom Rydberg tagging experiment [11,12]. This results in a high temporal and thereby kinetic energy resolution, and a negligible recoil velocity.…”

Laser ionization detection of O($^3P_j$) atoms in the VUV; application to photodissociation of O$_2$

“…It is, for instance, possible to detect laser-induced fluorescence after this excitation step [10]. Another method uses a second laser with a wavelength of 305 nm to excite the intermediate 3s state to high-lying Rydberg states which are then field ionized in a time-of-flight O-atom Rydberg tagging experiment [11,12]. This results in a high temporal and thereby kinetic energy resolution, and a negligible recoil velocity.…”