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

Abstract

Detection of O( 3 P j ) atoms using one-photon resonant excitation to the 3s 3 S o 1 state at ∼130 nm followed by near-threshold ionisation, i.e. 1 + 1' resonance-enhanced multi-photon ionisation, has been investigated. The aim was to achieve low ion recoil, improved sensitivity, and reliable angular momentum polarisation information, with an as simple as possible laser setup. An efficient 1 + 1' scheme has been found where the VUV light for the first step is generated by difference frequency (2ω 1 − ω 2 ) VUV generation, and the ionisation step 1' uses 2ω 2 around 289 nm. The presented scheme induces 9 m/s recoil of the O + ion using a two-dye laser system, and zero recoil should be possible by generating 302 nm radiation with a third dye laser. While this approach is much more sensitive than a previous 1 + 1' scheme using 212.6 nm for the 1' step, we found that the relatively intense radiation of the 2ω 2 beam does not saturate the 1' step. To test the ability of this scheme to accurately determine branching ratios, fine structure yields, and angular distributions including polarisation information, it has been applied to O 2 photodissociation around 130 nm with subsequent O( 3 P j ) fragment detection.

High-Resolution Imaging of C + He Collisions using Zeeman Deceleration and Vacuum-Ultraviolet Detection

“…Noteworthy species like OH, CO, NH 3 , and CH 3 possess well-known VUV transitions, − although for some the intermediate state is strongly predissociative, and it remains to be seen how efficient and state-selective near-threshold multicolor REMPI schemes are best implemented for these species. Furthermore, making use of the recently reported near-threshold VUV-based REMPI schemes for H/D or O­( 3 P ) atoms, our approach provides a pathway to high-resolution and low-energy investigations of elementary reactive scattering processes that produce O or H atoms, such as C + O 2 → CO + O ,, or complex-forming reactions between Zeeman decelerated atoms and H 2 molecules. − …”

“…30,56 Together with the use of VUV light for REMPI detection, this opens up new perspectives for detailed experimental investigations on a variety of scattering processes. For example, the recently reported near-threshold VUV REMPI schemes for H/D 57 or O( 3 P ) atoms 58 provide the interesting opportunity to investigate elementary reactive scattering processes, such as C + O 2 → CO + O 48,59,60 or complex-forming reactions between Zeeman decelerated atoms and H 2 molecules. [61][62][63] A promising candidate is the S( 1 D) + H 2 → SH + H reaction, for which distinct resonance features have been predicted to occur at low energies in both ICSs and DCSs.…”

Imaging Resonance Effects in C + H2 Collisions Using a Zeeman Decelerator

“…The sensitivity and attained collision energy range are similar to those in recent experiments employing Stark decelerators, which have proved to probe theoretical models with exceptional accuracy and, for example, enabled detailed characterizations of scattering resonances , as well as revealing novel scattering mechanisms in bimolecular collisions. , While the technique of Stark deceleration is limited to molecules that have an electric dipole moment, the method of Zeeman deceleration utilized here can be applied to a large class of paramagnetic species. , Together with the use of VUV light for REMPI detection, this opens up new perspectives for detailed experimental investigations of a variety of scattering processes. For example, the recently reported near-threshold VUV REMPI schemes for H/D or O­( 3 P ) atoms provide an interesting opportunity to investigate elementary reactive scattering processes, such as C + O 2 → CO + O ,, or complex-forming reactions between Zeeman-decelerated atoms and H 2 molecules. − A promising candidate is the S­( 1 D ) + H 2 → SH + H reaction, for which distinct resonance features have been predicted to occur at low energies in both ICSs and DCSs . Although a large body of work exists on these types of reactive systems, − ,,− there has been a continuous interest to study their scattering behavior under controlled and low-energy conditions − such as those provided by our combination of techniques.…”

“… 30 , 56 Together with the use of VUV light for REMPI detection, this opens up new perspectives for detailed experimental investigations of a variety of scattering processes. For example, the recently reported near-threshold VUV REMPI schemes for H/D 57 or O( 3 P ) atoms 58 provide an interesting opportunity to investigate elementary reactive scattering processes, such as C + O 2 → CO + O 48 , 59 , 60 or complex-forming reactions between Zeeman-decelerated atoms and H 2 molecules. 61 − 63 A promising candidate is the S( 1 D ) + H 2 → SH + H reaction, for which distinct resonance features have been predicted to occur at low energies in both ICSs and DCSs.…”