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xx
FIG. 5.5. 132
Phase diagram of p-H2/D2 mixture at low temperature based on eqs. 5.5 and 5.6.
FIG. 6.1. 142
CARS spectra of the S0(0) transition in both solid (a) – (c) and liquid (d) – (f) pH2 at
different temperatures as measured without an intra-cavity etalon. Measurements in
liquid were obtained at P = 2 bar. The frequency of the S0(0) line in the gas phase at
354.37 cm-1
is shown by a dashed vertical line.
FIG. 6.2. 143
CARS spectra of the Q1(0) line of pH2 at different temperatures as obtained with an intra-cavity
etalon. Traces (a) and (b) are in solid, whereas traces (c) – (h) are in liquid. All
spectra in the liquid were obtained at a constant pressure of 3 bar except trace (h) which
was measured at 9 bar and without an intra-cavity etalon.
FIG. 6.3. 144
Frequencies of the Q1(0) line in liquid pH2 at different temperatures and pressures as
indicated in the legend. Lines are linear fits to the results. Open circles show the results
at constant pressure in the cell of about 3 bar and at indicated temperatures.
FIG. 6.4. 145
Frequencies of the Q1(0) line in both solid and liquid pH2. Results in liquid were
obtained at a constant pressure of 3 and 9 bar, as shown by open squares and circles,
respectively, and were linearly extrapolated to SVP based on the results shown in Figure
3. Frequencies in liquid measured directly at SVP (solid squares) are also included for
comparison. The only previous measurement of liquid pH2 at 18 K and SVP is shown by
a star. Frequencies obtained in solid in this work and at SVP are shown by regular and
upside down triangles, respectively.
FIG. 6.5. 147
Density vs. temperature in solid (squares) and liquid (triangles) pH2. The dotted line
indicates the fitted density of liquid hydrogen, which includes an extrapolation into the
metastable range below the freezing temperature.
FIG. 6.6. 148
Q1(0) frequencies measured in this work for solid and liquid pH2 are shown by filled
squares. The experimental points in liquid were obtained at 3 and 9 bar and extrapolated
to SVP. Solid curves show the fits of both solid and liquid pH2 results to Eq. (6.1) with
identical parameters. The Q1(0) frequency in solid at SVP obtained by Kerr et. al is
shown by triangles. The dotted curve shows the estimated frequency in the liquid below
the freezing point, which was obtained from Eq. (6.1) using the estimated density of
liquid pH2 at low temperature as shown in Fig. 6.5.
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 20 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | xx FIG. 5.5. 132 Phase diagram of p-H2/D2 mixture at low temperature based on eqs. 5.5 and 5.6. FIG. 6.1. 142 CARS spectra of the S0(0) transition in both solid (a) – (c) and liquid (d) – (f) pH2 at different temperatures as measured without an intra-cavity etalon. Measurements in liquid were obtained at P = 2 bar. The frequency of the S0(0) line in the gas phase at 354.37 cm-1 is shown by a dashed vertical line. FIG. 6.2. 143 CARS spectra of the Q1(0) line of pH2 at different temperatures as obtained with an intra-cavity etalon. Traces (a) and (b) are in solid, whereas traces (c) – (h) are in liquid. All spectra in the liquid were obtained at a constant pressure of 3 bar except trace (h) which was measured at 9 bar and without an intra-cavity etalon. FIG. 6.3. 144 Frequencies of the Q1(0) line in liquid pH2 at different temperatures and pressures as indicated in the legend. Lines are linear fits to the results. Open circles show the results at constant pressure in the cell of about 3 bar and at indicated temperatures. FIG. 6.4. 145 Frequencies of the Q1(0) line in both solid and liquid pH2. Results in liquid were obtained at a constant pressure of 3 and 9 bar, as shown by open squares and circles, respectively, and were linearly extrapolated to SVP based on the results shown in Figure 3. Frequencies in liquid measured directly at SVP (solid squares) are also included for comparison. The only previous measurement of liquid pH2 at 18 K and SVP is shown by a star. Frequencies obtained in solid in this work and at SVP are shown by regular and upside down triangles, respectively. FIG. 6.5. 147 Density vs. temperature in solid (squares) and liquid (triangles) pH2. The dotted line indicates the fitted density of liquid hydrogen, which includes an extrapolation into the metastable range below the freezing temperature. FIG. 6.6. 148 Q1(0) frequencies measured in this work for solid and liquid pH2 are shown by filled squares. The experimental points in liquid were obtained at 3 and 9 bar and extrapolated to SVP. Solid curves show the fits of both solid and liquid pH2 results to Eq. (6.1) with identical parameters. The Q1(0) frequency in solid at SVP obtained by Kerr et. al is shown by triangles. The dotted curve shows the estimated frequency in the liquid below the freezing point, which was obtained from Eq. (6.1) using the estimated density of liquid pH2 at low temperature as shown in Fig. 6.5. |
