Characteristics and diagnostics of an ultrahigh vacuum compatible laser ablation source for crossed molecular beam experiments

Abstract

We present the design and the characteristics of an ultrahigh vacuum compatible laser ablation source which can be operated in a crossed molecular beam machine at pressures as low as 10−9Torr. This unit provides intense supersonic beams of up to 3×1013cm−3 reactant species (carbon atoms, dicarbon, and tricarbon) in the interaction region of a crossed molecular beam machine. Practical delay time windows between the pulsed valve releasing the seeding gas and the laser have been determined to be between 16 630 and 16645μs, i.e., firing the laser 150–165μs after the 80μs pulsed valve trigger. The concentration of the dicarbon and tricarbon clusters can be maximized/minimized by adjusting the laser focus (a tighter laser focus leads to an enhanced atomic carbon component) and the laser power (multiphoton dissociation). We achieved stable peak velocities between 800 and 3800ms−1 and speed ratios S of up to 6.

A Crossed Molecular Beam Study on the Reaction of Boron Atoms with Methylacetylene and Partially Deuterated Methylacetylene

“…[30][31][32] Briefly, a pulsed boron atom beam was generated in the primary source chamber by laser ablation of a boron rod at 266 nm (30 Hz; 5~10 mJ per pulse). [33] The ablated species were seeded in neat carrier gas (helium, 99.9999 %, Airgas) released by a Proch-Trickl pulsed valve at 4 atm backing pressure. It is important to stress that the boron beam is pulsed.…”

Crossed Molecular Beam Study on the Formation of Phenylacetylene and Its Relevance to Titan’s Atmosphere

“…The rotating carbon rod was mounted on an in-house built ablation source. 56 The 266 nm laser beam was focused by a 1.5 m quartz lens from the fourth harmonic (266 nm) output of a Spectra- actual pressure in the secondary source was about 5 × 10 -5 Torr. To optimize the intensity of each supersonic beam, which strongly depends on the distance between the pulsed valve and the skimmer, on line and in situ, each pulsed valve was placed on an ultrahigh vacuum compatible micropositioning translation stages with three stepper motors (New Focus).…”

Chemical Dynamics of the Formation of the 1,3-Butadiynyl Radical (C4H(X2Σ+)) and Its Isotopomers

“…At all velocities, the ablation beams contain dicarbon in its X 1 Σ g + electronic ground state as well as in its first electronically excited a 3 Π u state; at the present stage, the concentration of the singlet versus triplet states are unknown. 24 Although the primary beam contains carbon atoms and tricarbon molecules as well, these species were found not to interfere with the reactive scattering signal of the dicarbon-acetylene reaction at mass-to-charge ratios (m/ z) of 49 (C 4 H + ) and 48 (C 4 + ). Here, tricarbon reacts with acetylene only at collision energies larger than about 85 kJ mol -1 ; 25 signal from the reaction of atomic carbon with acetylene only shows up at m/z values of 37 (C 3 H + ) and lower.…”

“…Pulsed dicarbon beams were produced in the primary source by laser ablation of graphite at 266 nm by focusing 4-10 mJ per pulse at 30 Hz on the rotating carbon rod. 24 The ablated species were seeded in neat carrier gas (helium, neon, or argon, 99.9999%, 3040 Torr, Table 1) released by a Proch-Trickl pulsed valve. After passing a skimmer, a four-slot chopper wheel mounted after the ablation zone selected a part out of the seeded dicarbon beam, which crossed then a pulsed acetylene beam (C 2 H 2 ; 99.99% after removal of the acetone stabilizer via a zeolitic trap and acetone-dry ice cold bath) under a well-defined collision energy in the interaction region (Table 1).…”