International Symposium on Molecular Spectroscopy 63 rd Meeting

International Symposium on Molecular Spectroscopy 63 rd Meeting - - June 16 -20, 2008 Tel Aviv University U. Even “Advances in pulsed supersonic sources” 1. Supersonic beams start with a source (nozzle). 2. Source performance dictates entire system performance. 3. Source technology is often outdated and inefficient. 4. Large improvement is possible in signal levels. 5. Most systems can be retrofitted to achieve performance upgrade. 6. New experiments become feasible with source improvement.

Sonic Nozzle (pinhole) beam shape Simulation by Monte Carlo method (DSMC) Program developed by Dr. Graham Bird and is free http: //www. gab. com. au/ Wide beam (550 FWHM); Low on axis intensity

De Lavalle (or Bell) Nozzle 1. Designed for Maximum Thrust. 2. Exit Temperature is quite high. 3. A bad source for supersonic beams.

400 Conical Nozzle Simulation Narrow beam (200 FWHM); Higher on axis beam intensity (x 8 over Sonic Nozzle)

Comparison between Conical and Trumpet shaped Nozzles Low temperature achieved where the jet is at high density; important for clustering

Side remark: Acceleration in nozzles 1. Expansion shown for Argon. 2. The gas reaches 600 m/s. over a distance of 2 nozzle diameters in 1 microsecond. 3. The acceleration is enormous a>5*108 m/s 2 for Argon a>5*109 m/s 2 for Helium !! Interesting inertial effects in spectroscopy? ?

Structure of a pulsed valve: Miniaturization is the key.

Calculated magnetic field (~3 Tesla in 10 microseconds) Solving Maxwell equations for real boundary conditions and real materials

Construction of a single Magnetic stage in a magnetic slowing experiment

Trumpet Nozzle beam made visible by glow discharge (Neon)

Pulsed valve Temporal and Angular beam profile

Skimmers for High Intensity Beams 1. Campargue type skimmer for low intensity beams.

Campargue type Skimmer in high density beams

Long Conical Skimmer at High beam Intensity Large entrance hole, 250 full Angle, 50 mm length.

Overall system construction Tubo-Pumps Cryogenic Pulsed Valve Skimmer MCP Detector Dielectric Barrier Discharge source: 109 excited atoms/pulse after the skimmer

Arrival time distribution after ~1 meter flight.

Terminal kinetic energy distribution

Velocity of supersonic jets J. Chem. Phys. 118, (19), 8690 (2003)

Standard deviation of the velocity distribution

“Beam Temperature” in high intensity jets

Cooling of large Molecules in high intensity He jet Limit is set by Helium Condensation on the molecular surface J. Chem. Phys. 115 (5), pp. 2069 -2073, (1 Aug 2001). Aniline Rotation contour; T=0. 4 k

Photo electron spectroscopy of large clusters D. Neumark and O. Cheshnovsky Science 307, 93 (2005);

Laser alignment of cold molecules Stapelfedt H. PRL 100, 093006 (2008)

Growing Very large (and cold) Clusters Nakajima A. J. Chem. Phys. 128, 154318, (2008)

Slowing Helium to achieve high resolution spectroscopy of surfaces

Beam Slowing Results