Matt Johnson played a key role in the development of the derivation source and was always available to lend a hand or listen to my (mostly stupid) ideas. The resulting fragment ion is mass analyzed and detected where its intensity as a function of laser wavelength is. Current research activities on halide-solvent clusters and metal-ligand complexes as well as technological improvements of the apparatus are also discussed.
The high reactivity of the ions makes it difficult to generate sufficient ion concentrations for the traditional gas phase absorption spectroscopy.1. With this improvement, Oka was able to observe the v2 band of the H3+ ion in a DC discharge of hydrogen.2.
OUTLINE
The source code for OPODATA, the computer program that controls the scanning of our LiNb03 OPO, will be included in the appendix.
Experimental
THE ION BEAM APPARATUS
- Ion Generation
- TOF Mass Spectrometer
- Fragment Ion Detection
The gas mixture is sent to the stagnation chamber of the pulse valve through the gas inlet line. P IPb exceeds the critical value of -2.1.3 The most important consequence of expansion being supersonic is supersonic cooling. Placing the ion source away from the skimmer causes a reduction in the ion signal.
Most of the components that make up the TOF mass spectrometer are shown in Figure 1. The operation of the TOF mass spectrometer will be described for the case of positive ions (conversion to a negative ion mass spectrometer can be accomplished simply by reversing the polarity and potentials on the ion optics). .
OPTICAL PARAMETRIC OSCILLATOR
- Low Resolution Configuration
- High Resolution Configuration
- Separation of the Signal, Idler and Pump Beams
- Wavenumber Calibration
In most of our experiments, the low frequency component of the OPO output (i.e. the idler) is used to excite the ions. The optical cavity of the OPO is single resonant, with the high frequency wave ("signal") being the resonant wave. One port measures the pulse energy of the OPO beam by digitizing the output of a Molectron J25LP joule meter.
Another port measures the photoacoustic signal whose spectrum is used to calibrate the wave number of the OPO beam. OPODATA facilitates different scanning algorithms for the three different configurations of the OPO (low resolution, medium resolution and high resolution configurations).
SYSTEM OPERATION
- Ion Apparatus Operation
- The Complete Experiment
C goes TIL-high, triggering the TOF pulse repeller circuit, marking the start time for ion flight in the mass spectrometer. Channel C is also connected to the trigger input of the mass gate controller, which has an internal delay circuit.) The resulting TOF mass spectrum is collected by the LeCroy waveform digitizer, which begins its data acquisition upon receipt of a trigger pulse from the D channel (usually set at 20 ps after the C channel pulse). When the laser is externally activated, channel A of the EG&G turns on the flash lamp and channel B activates the laser turn on with switch Q. In addition to activating the pump laser of the OPO, it can also control the pulse of the ion apparatus by connecting its channel output T0 with the externally triggered input of the Stanford Research System delay generator.
Thus, the SRS becomes a slave delay generator which is externally activated by the EG&G master, and the adjustable delay time responsible for beam synchronization is the delay between the A channel of the SRS and the input of the external SRS register. The infrared ion spectrum is recorded by increasing the wavenumber of the OPO beam and averaging the photofragment intensity for 400 pulse events at each OPO wavenumber.
The etalon and lattice tilt in the plane of the figure, and the LiNb03 crystal tilts out of the plane. The pump beam is located at 9394 cm·1. The ordinate of the spectrum is the computer's steady-state wavenumber, and the numbers above the peaks are the steady-state wavenumbers of the corresponding HCl rovibrational transitions. Comparing these numbers with the ordinate shows that the computer wavenumbers deviate from the experimental values by 0 - 2 cm·1•.
IDLER, ~ SIGNAL, ~ YAG OUT I OUTPUT COUPLER
SiH 7 +
- EXPERIMENTAL
- RESULTS AND DISCUSSION
- COMPARISON WITH NEW AB INITIO RESULTS
- CONCLUSION
- REFERENCES
- RESULTS
- DISCUSSION
- Intracluster Reaction
- CONCLUSION
- REFERENCES
- b) Simulation
This band has distinct P, Q, and R branches, with the Q branch centered at 3866 cm-1. The only photofragment ion observed was SiH5+, indicating that the photodissociation process involved was SiH7+ -7 SiH/ + H2. • Because of the wide . This structure should result in two H-H stretch bands: the symmetric and antisymmetric combinations of the two H2 stretches. Both calculations obtained a large transition intensity for the antisymmetric combination mode of the H2 trajectory, and
The discrepancy between theory and experiment is in the binding energies of silicon hydride clusters (Table II). In Si2H7+, for example, two Si atoms are said to bond through an H atom with the structure H3Si-H+-SiH3• The structure and new bonding of these new species can also be studied by multiphoton dissociation techniques. These values lead to the binding energy of the N02+•H20 complex in the range of 5 to 19 kcal/mol.
Infrared spectra were obtained by measuring the intensity of the photo fragment as a function of the laser wavelength. The experimental results on NO/(H20)n clusters will be described in terms of the cluster size, n. The locations of the band centers are summarized in Table 1.). The second isomer, a covalently bonded (H0)2NO+, is calculated to be 20 kcal/mol higher in energy.6 The (scaled) ab initio 0-H stretching frequencies, which are very different between the two isomers, are listed in table II.
Consequently, the observed bands are assigned as the symmetric and antisymmetric stretches of the H O ligand, respectively. The predicted selection rules are consistent with the observed spectra, which show a single maximum (with two shoulders) in the 3626 cm·1 band and two closely spaced maxima (Q-branch features) in the band at 3704 cm·1 ·. ab initio rotation constants and a rotation temperature of 80 K (characterized by previous experiments), we simulated the band contours of these two transitions.9 The general characteristics of the simulated rotation contours are consistent with the experimental results (Figure 4). Therefore, the positive charge should now be in the form of H30+, to minimize the total energy of the clusters.
According to Fehsenfeld eta/. the interaction between the products H30+(H20) and HN03 should lead to the stable complex H30+•(H20)•HN03. We did not observe this in our experiment. For the last image, the ordinate is the photofragment yield from the HN03 loss channel of the n = 4 cluster.
HCION0 2 +
- EXPERIMENTAL
- RESULTS
- DISCUSSION
- CONCLUSIONS
The catalytic cycles responsible for ozone reduction are now well defined.4 The most important cycle among them is the ClO:5 dimer mechanism. Finally, small portions of Cl 2 O were condensed in a flask containing N 2 O 5 at -196 oc;. the flask was then warmed to -25 oc to allow reaction. was transferred to a flask at -196 oc by heating the reaction flask to -78 oc. impurities in the product mixture, which could easily be seen as a white solid in the yellow supernatant at about −70 °C, were removed by vacuum distillation. The strongest band is centered at 3582 cm·1, while a band of about half the intensity is observed at 3386 cm·1• the weakest band appears at 3712 cm-1• The intensity of each of these bands depended linearly on laser flow. .
This suggests the existence of an intact HOCl group within HClONO/. The possible existence of such a group, combined with the observation that the photofragment ion of HClONO/ is NO/. mle=46), leads us to suppose that the structure of protonated chloronitrate is as follows. This band assignment is then consistent with the conclusion that the structure of protonated chloronitrate is NO/*(HOCl). The location of the band is in excellent agreement with the scaled 0-H strain frequency of 3379 cm·1 from the ab initio calculations (at MP2-TZ2P level) for the.
Our band assignments are supported by our previous studies on the vibrational spectrum of protonated nitric acid, H2NO3+. Examination of these spectra should provide confirmation for the existence of the second isomer. The crucial step in the above reaction is protonation of the ClO group and formation of the complex, which should lead directly to the formation of HOC!.
An important prediction of the proposed reaction is the existence of a nitronium ion at or near the surface. Our experimental observation of the complex NO/•(HOCl) upon protonation of chlorine nitrate provides strong support for the ionic mechanism of ClONO2 reaction on PSC surfaces proposed by Nelson and Okumura. In the middle panel, proton transfer to chlorine nitrate occurs, leading to the formation of the weakly bonded complex of HOCl and NO.
PROPOSED MECHANISM FOR CION0 2 DECOMPOSITION ON ICE
Ongoing Research
- METAL-LIGAND COMPLEXES
- METASTABLE ELIMINATION
- REFERENCES
Initial studies of Cl.(H2O) show that the 0-H portion of the water ligand . kcal/mol) for the pseudo-rotation in the plane of H20 in this cluster. Therefore, low-resolution IR spectroscopy can provide ligand vibrational frequencies, providing a test for the high-level ab initio calculations performed on metal-ligand complexes. Will the vibrational excitation of a strongly bound H2 ligand cause the weakest bound H2 ligand to be released from the cluster?
We have previously tried to study Co+-(H2)" clusters and generate them by sputtering the discharge electrodes with little success. With this configuration, photofragment ions will have a different kinetic energy as well as a separate trajectory from that of the metastable ions, which are mostly generated in the time-of-flight section.Second, since reflectron fields are tilted with respect to the beam axis, dissociation within the reflectron causes a transverse deviation of the photofragment beam.
This device is positioned along the path of the ion beam, with the laser interaction point lying in the middle of its central region. We choose that the electric fields of the meta-deflector E (facing down) are in the first. Specifically, if the kinetic energy of the parent ion is Ek, the equivalent field-free length between the meta-deflector and the detector is D, the transverse separation ~z.
With an active area of the MCP detector of about 2 em in diameter, the separations caused by the meta-deflector are large enough to allow the detection of photofragments, while the metastable ions miss the detector completely. Two different implementations of the meta-deflector, which produce electric fields close to the ideal distribution, are discussed in the following paragraphs. This can be easily corrected by slightly increasing the electric field in the second region, which introduces a small net upward acceleration for the photofragments.
VAPORIZATION LASER
The wavenumber is determined by the lattice position NGrating } { via a spline function WNNG (inverse function is NGWN) } {2.
