I would like to thank Earl Potter, the (un-)lucky inheritor of the apparatus I helped build, for his unselfish assistance during my last experimental effort. This thesis is the fruit of the seed of life, which they planted in my heart and mind.
CHAPTER I
GENERAL CONSIDERATIONS
A recent overview of the applications in the field of chemistry can be found in Refs. The pulse energies of the laser oscillators described above are of the order of lnJ.
SYSTEM DETAILS
The observed linewidth(s) will be a convolution of the laser spectral width and the intrinsic absorption linewidth. This advantage is achieved at the expense of additional complexity in the generation of the second adjustable light source. A schematic of the YAG and dye oscillators and amplifier arrangement is shown in Figure 4.
The orientation of the laser polarization is that of the P polarization with respect to the face of the block. The requirements of some of the experimental efforts described in the following chapters and in L.R. Such temporal broadening arises from the dispersion of the refractive index in the glass, suprasil, and the coloring medium of the amplifier.
Alternatively, the output from the x 10 amplifier is fed into a 100MHz transient digitizer (LeCroy model TR8818). First, the chosen molecule must have an absorption at the wavelength of the pump pulse. The oxygen atom otherwise reacts with the triplet state of the dye and forms a useless photoproduct.
This schematic of the EI-TOFMS, shown in the previous image, provides additional details of the design. This schematically outlines the setup of the detection electronics for the LIF and TOF signals.
TOF MS
INTRODUCTION
Comparison of the direct time-resolved results with steady-state angular distribution measurements can then be made. In this letter, we would like to report our first results on the femtosecond time resolution of the primary photofragmentation (on the repulsive surface) of the reaction. In these experiments, as detailed in Figure 1, a femtosecond pulse (photolysis pulse) initiates the dissociation by exciting ICN (with a well-defined E-field polarization direction in the laboratory frame) after the continuum absorption of the repulsive.
These experiments provide a direct view of the bond breaking process and illustrate some of the difficulties inherent in the earlier indirect methods. The response function of the system is obtained by replacing the ICN-LIF cell with an N,N-diethylaniline (DEA) ionization cell and generating a resonance-enhanced 1+1 ionization transient. This form of delayed rise is similar to the observation of Smith et al.5 on the picosecond time scale.
We used the REMPI transient as the response function of the system for fitting the ICN transient using a non-linear least-squares single exponential fitting routine. It has been shown that the experimentally observed shift cannot be achieved while maintaining the shape of the REMPI transient. The above processing of the data confirms that the REMPI transient is the system response and that the observed shift is due to the final r of 600 ± lO0fs.
RESULTS AND DISCUSSION
Inclusion of these dynamic effects is essential to understanding the rebound process, and we hope. Parallel (II) and perpendicular (1.) refer to the orientation of the polarization of the photolysis pulse to the probe pulse. Schematic representation of the ICN state structure related to the photodissociation processes considered.
The rotational anisotropy plot in Fig. 16b in Section 2 undergoes dynamic evolution on a time scale of 0.5 lps. The data set is the same as that shown and analyzed in Figure 2 of this chapter. A similar display of the rotational anisotropy of the ICN data would be interesting.
The last point may be justified by two features of the experimental conditions. Pump probe time resolved the formation of the CN product after the photofragmentation of ICN. Same as Ala, except the relative polarization of the pump and probe beams is perpendicular.
INTRODUCTION
The (exponentially) increasing splitting of the relevant spectroscopic potential surfaces can explain the red-wing emission. The application of the pump-probe method to the study of single-molecule dissociation dynamics is illustrated in Figure 1. Consequently, more light with a wavelength within the blue part of the probe frequency band is projected towards the detector.
Second, many studies of scalar and vector asymptotic properties of the dissociation process have been measured. This will be followed by a section dealing with HOOH spectroscopy and the electrostatic properties of the OH radical. A brief summary of the entire experimental arrangement with an additional explanation of the more essential aspects will suffice.
The second harmonic of the synch-pumped dye laser light is used as the probe pulse. The output of the dye laser is injected into a Nd:YAG laser-pumped four-stage dye amplifier. The duration of the entry pulse was 5ps and the exit pulse is measured as 5.5ps FWHM Gaussian.
SPECTROSCOPIC STUDIES OF HOOH
Attempts have been made to calculate the energies of the excited states of HOOH. It was concluded that the steep section of the PES generates the angular momentum of the fragment. However, these studies demonstrate that the torsional dependence of the excited state potential is the main source of fragment rotational excitation.
The source of the disagreement is attributed to a shortcoming in the potential used in Ref. Klee et al.40 explain this result by saying that the spin angular momentum of the fragments arises from a strong spin dependence for the excited electronic surface 1 Au. It is found, through the full N 1 =N 2 correlation decomposition of the two OH36 products, that repulsion along the 0-0 bond (slightly separated from the centers of mass) will produce a torque and spin excitation.
Also, the OOH bending mode dependence of the 1 Au PES will cause some rotational excitation. These authors estimate that the rotational excitation contributes approximately 25% of the total rotational energy for the non-torque processes. The Hund case (b), which applies to the 2E levels (e.g. A=0), implies a coupling of the electronic spin and the nuclear rotational angular momentum N.
RESULTS
The data of Figure 2c are measured for a spectral decay of 4cm-1 in the red of the Q1(1) resonance. In addition to the issue of having the correct functional form for the response function is the uncertainty of the point t=O. Therefore, the uncertainty in the fitting results is important for the magnitude of the observed effects.
Since the transient feature appears on both sides of the resonance, it is possible for it to appear abruptly. The maximum transient amplitude appears approximately at the inflection point of the on-resonance rise. The relative amplitude of the on resonant signal to the spectrally distorted value is found to be approximately 5:1 at the resonant frequency.
The positions of the fitted line shapes were obtained from the known frequencies for the relevant OH transitions. The origin for the perturbed spectral shape is centered on the value of the transition frequency of nascent OH. This is decided so that the relative amplitudes result in a consistent presentation of the perturbed spectral data.
DISCUSSION
Arguments will be presented for the implication that these observed results have for the mechanism of dissociation. The notion that the current experimental observations do not simply originate from the exponential spread of V 1 and V 2 potential surfaces can be reinforced. These conditions imply that the current picosecond probing process samples the nearly asymptotic region of the potential surface.
The analysis of the long-range interactions can be undertaken by assuming that the dissociation process yields two groups of products. Margenau49 described a method for calculating the resonance energies for rigid linear dipoles and quadrupoles. The degeneracy of the state vector implies that the resonance values are obtained by solving the determinant47.
The coordinate inversion changes the sign of the second and third terms of Eq. 5.6) (as well as the first term as implicitly mentioned in the preceding paragraph). The spherical harmonic addition theorem51 can be used to evaluate the spatial integrals of the shape. In fact, the magnitude of the difference for the data sets would yield the previously measured asymptotic alignment.
CONCLUSIONS
A schematic drawing of the pump-probe as applied to the study of direct (electronic) dissociation. The OH laser-induced fluorescence (LIF) signal is monitored as a function of the relative. A picosecond pump pulse prepares the HOOH in the fourth overtone level of the OH stretching mode.
The only essential difference in experimental conditions for the two measurements is the change in pump wavelength. This figure shows a decay curve for the R,(I)OH product transition (pump wavelength: 6157 Å, pressure: 300 mTorr), which is the lifetime of the OH in the excited A 2 . The fast and slow component lifetimes for the N = 2 transients are shorter than for N = I and the contribution of the fast component to the total amplitude becomes larger (that is, the fraction increases).
These calculations showed that most of the vibrations are strongly coupled (on the time scale of the reaction). This means transferring the thermal distribution of the ground state to the level of the fourth overtone. The conserved quantum numbers limit the phase space domain (for given E and J).
This paper, the second in the series, presents picosecond time-resolved studies of the overtone (v0 H = 5). This may depend on the magnitude of the rotational energy's contribution to the total reaction energy.
