The members of the instrument shop (Bill Schuelke, Tony Stark, Guy Duremberg, Bill Schuelke (the younger). The second appendix discusses an electron impact study of the electronically excited states of 1,3,5-cycloheptatriene. Finally, a preliminary study of the two-photon -resonance-enhanced multiphoton ionization of p-xylene is reported.
Next, the scattered electron intensity distribution is measured. as a function of the lost energy with respect to the incident electron beam energy. Therefore, the energy loss spectrum corresponds directly to the excitation energies of the sample gas. The resolution of the electron impact spectrum is significantly worse than that of an optical spectrum at energies below the vacuum ultraviolet.
A description of the apparatus used to obtain the electron impact spectra of the molecular systems reported in this thesis is included in Section 2.
EXPERIMENTAL 1 Introduction
Translation of this was accomplished using the NDTOMT program (not the program previously described by fli'cker5 and Mosher4). Electrons leaving the monochromatic are accelerated by the twelve-to-one acceleration system provided by l:tM2 and M4. The deviations of of the optimal monochromator potentials from the calculated ones may be partly due to the influence of the magnetic field.
Blocking part of the capillary array and adding a diffusion pump to the optical chambers can alleviate this problem. The transmitter and receiver clocks are connected to the output of counter 2 of the 8253. The special block i is set to the base address ECOOH using jumpers between pins 5 and 12, pin 6 and 11, pin 7 and 10, and pi_ns 61 and 62, (Note: User the RTI 1201 manual does not contain any problematic errors regarding address selection.The preceding connections are correct.)_ DACs can be configured for any of several different voltage ranges.
The MSC 8001, which only provides BK RAM, does not have the data storage capacity for 4096 channels (.resolution of a 16-bit DAC) with up to one million counts per channel t3 bytes per channel).
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These outputs are connected to a 16-way DI'P switch (.A7} that allows selection of the BK memory block. These outputs are connected to four levels of a DTP switch (A12} that allows switch selection of the address for RAM The outputs of the PROM addressing DIP switch (A7) are connected together and connected to 5 volts through an lKn resistor.
Currently, only three I/O pins are used to provide gate control for the 8253 programmable interval timer. Power for the input side of the amplifier is provided by the ±15 V DC/DC converter outputs on the RTl 1201. The output stage of the isolated amplifier is powered by a Burr Brown model 700 tsolated DC-to - DC converter.
At the heart of the circuit is ·1 Burr Brown model 710 quad isolated DC/DC converter.
EJB ~
In addition, the reduced volume allows the PAD to be mounted on the main flange of the instrument, making the device less susceptible to EMI pick-up.
ODDO
RESULTS AND DISCUSSION
The energy resolution, as measured by the full width at half maximum (FWHM) of the elastic peak was. As discussed in the introduction, the ratio of the weights of spin-forbidden to spin-allowed transitions increases significantly as the scattering angle increases. This nonnalization provides a clear representation of the fraction of the spin-forbidden transitions for the high-angle spectra.
We have performed extensive tests to ensure that the difference spectra obtained in this way are not simply artifacts of the subtraction technique. The overall characteristics are unchanged by varying the angle of the high-angle spectrum used in the descent and the impact energy used for both the high- and low-angle spectra. To understand 1 spectrum, we will consider different regions of energy loss separately.
Frosch and Robinson using the vibrational data obtained from these results and their own estimates of the gas phase X 2. The intensity of these peaks relative to the y(0-0) intensity at 5.47 eV increases by more than one order of magnitude when the beam angle increases from 20° to 80°. The low-angle spectrum was unanalyzed to the 8.36 eV feature of the high-angle spectrum.
A potential uranium isotope separation scheme involves isotope-specific vibrational excitation of the 11 3 235UF6 mode. In order to determine the positions and nature of electronically excited states that might prove important for such a scheme, the electron impact spectrum of UF 6 was studied. B From the point of view of ligand field theory, it is assumed that the valence electrons of the central metal atom (5f, 6d and 7s electrons of uranium and 5d and 6s electrons of tungsten) are transferred to the fluorine atoms, forming a complex of the form M&+ F:-.
Similarly, attempts to correlate the electron impact DCS with the magnitude of the spin-orbit interaction have been limited to the study of Xe by Williams, Trajmar, and Kuppermann. Koelling et al., 11 on the basis of relativistic SCF Xa calculations, attribute both to dipole-allowed transitions.
DISCUSSION
26 Since it must correspond to the value of f opt (absolute) obtained from the data of ref. This factor is independent of the transition under consideration and is therefore the same for the 13. The similarity of the UF6 spectrum above 5 eV energy loss with that of WF 6 indicates that the primary contribution to the spectrum in this region is also due to are to transitions of fluorine ligand a and 1T.
86 e V in UF 6 compared to the corresponding features in WF 6 may indicate an additional contribution in UF 6 from the ligand to the 5f orbital excitations. Using the orbital energy ordering for UF 6 as well as the excitation energies calculated by Koelling et al. the ordering in this molecule is the same as for the corresponding orbitals in UF6• Transitions below 5.
However, comparison with our WF 6 results indicates that a significant part of the intensity of this feature is due to excitation to uranium 6d (4y sg, 2y 7g) orbitals (see Fig. 1). 75 eV in WF6 is clearly different from the other features in the spectra. This is due to the fact that the ligand-field interaction for 5f orbitals is significantly weaker than for 6d orbitals and is expected to be of the same order of magnitude as the spin-orbit interaction, weakening the argument for an LB coupling scheme.
Assignments of the spectra of both UF6 and WF6 have been proposed using the theoretical results of Koelling et al.11. Valence orbital energy ordering for UF6• The symmetry designations listed below oh are those appropriate for the octahedral point group, while those below oh are appropriate for the octahedral double point group. Integrated intensities of several electronic transitions in UF6 divided by the integrated intensity of 5.
Characteristic 8 eV as a function of scattering angle 8 at an incident electron energy of 50 eV; transition energies for each of the curves are shown. Integrated intensities of several electronic transitions in WF6 divided by the integrated intensity of 8.
8 (DEG)
49 eV in the 80° spectrum, which is not observed in the 10° spectrum and has not been previously reported. Unfortunately, it is only possible at present to state that our results are consistent with assigning transitions observed between 5.5 and 7.25 and between 7.5 and 8.0 eV in both optical and low-angle electron impact spectra to singlet+ triplet- excitations. X ~ + C A' excitation occurs at 8.03 eV and that the previously reported value of 8.139 actually includes a quantum of the bending state.
The long progression in the bending mode is due to the decrease in the bond angle of the C 1A' state (a= 141°) relative to that of the ground state (180. A progression in the c=N stretching mode (v 3) ) is clear with additional members of the progression that occurs at 9.03. A summary of the energies of features observed in hydrogen cyanide as well as assignments of those features is given in Table 1.
The spectrum of acetonitrile in the energy loss range from 4.6 to 9.3 eV is very similar to that of hydrogen cyanide. The weak features observed in our spectra at 5.5 and 6.7 eV have not been observed before. The similarity of the spectrum of acetonitrile in this region to that of hydrogen cyanide, which has been attributed. overlapping transitions TI + TI and n + TI support its assignment.
Stradling and Loudon suggested assigning the peak observed at 9.04 eV to TI + 3s excitation. The spectrum of malononitrile in the energy loss region below 9.5 eV is very similar to the spectra of hydrogen cyanide and acetonitrile. Highly overlapping features are observed in the low-angle spectrum with apparent maxima at about 6.5 and 7.8 eV and an intense
This feature was tentatively assigned as a singlet + triplet excitation and corresponds to a feature observed in the acetonitrile spectrum at 6.1 eV, which Fridh16 proposed to be due to an impurity. The features observed in our spectra at around 6.5 and 7.8 eV have not yet been described, although the feature reported by Stradling and Loudon at 6.4 eV may correspond to the 6.5 eV feature we observe. This suggests that the feature observed at 25 eV, 10° is due to the n + n overlap observed in the previously discussed alkyl.
We have assigned both valence and Rydberg transitions observed in acetonitrile, malononitrile, propionitrile, and butyronitrile to strongly depend on the similarities of the spectra to hydrogen cyanide.
