Experimental generation of a cw cold CH3CN molecular beam by a low-pass energy filtering

Abstract

We generate a continuous-wave (cw) cold methyl cyanide (CH₃CN) beam by using an L-shaped bent quadrupole electrostatic guide (i.e., by a low-pass energy or velocity filtering), and use a photo-ionized time-of-flight mass-spectrometer method to experimentally measure and study the dependences of the longitudinal and transverse temperatures of the guided CH₃CN beam and its guiding efficiency on the guiding voltage. We find a new scaling law: the longitudinal and transverse temperatures (T_z,T_ρ) of the guided CH₃CN beam are proportional to the guiding voltage (T_z,T_ρ ∝ V_guide), and further verify another scaling law: the molecular guiding efficiency η is proportional to the square of the guiding voltage (η ∝ V²_guide). We also obtain some simulated results consistent with our experimental ones. We also measure the divergent angle of the output molecular beam and study its dependence on the guiding voltage. Our study shows that when the guiding voltage is V_guide = ±1 kV, a cw cold CH₃CN beam with a longitudinal temperature of ∼500 mK and a transverse one of ∼40 mK can be generated by our L-shaped electrostatic guide. The divergent angle of the output CH₃CN beam is about 16.4° as V_guide = ±4 kV. It is clear that such a resulting cold molecular beam has some important applications in the fields of cold molecular physics, physical chemistry and chemical physics, etc.