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210
at both ends and is also connected to a poppet. The faceplate has a CF groove and in the
middle it has a hole from 0.25 to 1.0 mm diameter depending on the part number.
Without electrical power, the poppet is pressed against the nozzle orifice and the valve is
closed. Upon triggering, the driver IOTA-1 generates a 300 V electrical pulse of
approximately 180 μs duration time in order to open the valve and then maintains about
28V to hold the valve open.
Poppet Changing Procedure
Upon operation of the pulsed valve, the poppet strikes against the stainless steel
faceplate with every pulse. This process causes a degradation of the poppet at which time
the valve will eventually start to leak or the droplet flux may decrease due to a change of
geometry of the poppet. In order to change the poppet, the pulsed valve should be taken
out of the He apparatus. Once the valve is disconnected from the He apparatus, the
pulsed valve is opened by inserting two nails into two opposite holes in the faceplate and
holding the nails using a vice. With the pulsed valve engaged, which pulls poppet away
from faceplate in order to prevent damage, the body is unscrewed from the faceplate
using a wrench inserted in between the faceplate and the body. The driving rod and two
springs are removed from the valve and the poppet is removed from the inside driving
rod and changed for a new one. When assembling the pulsed valve, it is necessary to
take special care in order to avoid scratching of the poppet surface upon screwing
together the body and the faceplate. Following the driver manual, one should set the
Object Description
| Title | Infrared and Raman spectrosopy of molecules and molecular aggregates in helium droplets |
| Author | Sliter, Russell Thomas |
| Author email | sliter@usc.edu; sliterr@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2011-04-21 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-04-26 |
| Advisor (committee chair) | Vilesov, Andrey F. |
| Advisor (committee member) |
Reisler, Hannah Kresin, Vitaly V. |
| Abstract | This dissertation covers several different aspects of spectroscopy of molecules and molecular clusters embedded in low-temperature matrices, such as helium droplets. First, details on the formation and optimization of He droplets will be discussed. A new method of measuring droplet sizes for cw nozzle expansions using mass spectrometry was developed. The results of the measurements of the sizes of the droplets in pulsed expansion as a function of temperature will be described. Details on the electron-impact ionization of He droplets will also be discussed as well as a simple method of modeling the ionization and excitation of He atoms in the droplet. In addition, preliminary measurements on the size distribution of He droplets produced at very low temperature of 5 – 7 K in continuous expansion will be addressed.; Using matrix isolation in He droplets, vibrational spectra of clusters consisting of para-H₂ or para-H₂/D₂ have been obtained using coherent anti-Stokes Raman spectroscopy (CARS). The vibrational frequency of para-H₂ molecules obtained upon expansion of neat para-H₂/D₂ gas or liquid was found to be very similar to that in bulk solid samples having equal composition. On the other hand, spectra in clusters obtained upon expansion of 1% para-H₂/D₂ clusters seeded in He are liquid and have a considerable frequency shift, which indicate phase separation of the two isotopes in clusters at low temperature. The onset of phase separation in para-H₂/D₂ mixtures is predicted at approximately 3 K providing further evidence of super-cooled liquid hydrogen clusters.; To address the Raman spectra observed in liquid H2 clusters, vibrational and rotational spectra of bulk liquid para-H2 at temperature of T = 14 – 26 K and of solid at T = 6 – 13 K have been obtained using coherent anti-Stokes Raman scattering technique. The vibrational frequency in the liquid increases with temperature by about 2 cm⁻¹, and the shift scales with the square of the sample’s density. An extrapolation of the vibrational frequency in the metastable para-H₂ liquid below the freezing point is discussed. The results indicate that the vibron hopping between the molecules is active in the liquid, similar to that previously found in the solid.; Matrix isolation has also been performed in argon solid matrices based on a custom-made cryogenic optical cell. Single water molecules have been isolated in solid Ar matrices at 4 K and studied by ro-vibrational spectroscopy using FTIR in the regions of the v₁, v₂, and v₃ modes. Upon nuclear spin conversion at 4 K, essentially pure para-H₂O was prepared followed by subsequent fast annealing generating ice particles. FTIR studies of the vapor above the condensed water upon annealing to T ≥ 250 K indicate fast re-conversion of nuclear spin to equilibrium conditions. Our results indicate that nuclear spin conversion is fast in water dimers and larger clusters, which preclude preparation of concentrated samples of para-H₂O, such as in ice or vapor. |
| Keyword | Helium droplets; laser spectroscopy; matrix isolation; superfluidity; clusters |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3778 |
| Contributing entity | University of Southern California |
| Rights | Sliter, Russell Thomas |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Sliter-4404 |
| Archival file | uscthesesreloadpub_Volume23/etd-Sliter-4404.pdf |
Description
| Title | Page 234 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 210 at both ends and is also connected to a poppet. The faceplate has a CF groove and in the middle it has a hole from 0.25 to 1.0 mm diameter depending on the part number. Without electrical power, the poppet is pressed against the nozzle orifice and the valve is closed. Upon triggering, the driver IOTA-1 generates a 300 V electrical pulse of approximately 180 μs duration time in order to open the valve and then maintains about 28V to hold the valve open. Poppet Changing Procedure Upon operation of the pulsed valve, the poppet strikes against the stainless steel faceplate with every pulse. This process causes a degradation of the poppet at which time the valve will eventually start to leak or the droplet flux may decrease due to a change of geometry of the poppet. In order to change the poppet, the pulsed valve should be taken out of the He apparatus. Once the valve is disconnected from the He apparatus, the pulsed valve is opened by inserting two nails into two opposite holes in the faceplate and holding the nails using a vice. With the pulsed valve engaged, which pulls poppet away from faceplate in order to prevent damage, the body is unscrewed from the faceplate using a wrench inserted in between the faceplate and the body. The driving rod and two springs are removed from the valve and the poppet is removed from the inside driving rod and changed for a new one. When assembling the pulsed valve, it is necessary to take special care in order to avoid scratching of the poppet surface upon screwing together the body and the faceplate. Following the driver manual, one should set the |
