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RISS 인기검색어
- 검색키워드
- 저자 : Peppernick, Samuel John (검색결과 1 건)
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United atoms to superatoms and the isoelectronic principle
Peppernick, Samuel John The Pennsylvania State University 2009 해외박사(DDOD)
The work described in this thesis pertains to the photoelectron spectroscopy of negatively charged atomic ions and their superatomic counterparts. The molecular ions studied in this work, TiO-, ZrO -, and WC- can be interpreted as superatomic manifestations of the respective isoelectronic elements appearing on the periodic table. The superposition principle, in the context of the unified atom picture from molecular orbital theory, allows for the assignment of molecular electronic transitions to be referenced to the atomic frame. This approach represents a novel method of determining the electronic state origins of transitions appearing in the photoelectron spectra of molecular anions by directly comparing the known spectroscopy for the isoelectronic element. In Chapter 3, a remarkable correspondence is presented between the separate PADs produced independently by TiO- and Ni- , suggesting the bound ionic state of the diatomic is mimicking that present in the negative atomic ion. Application of the beta-wave approach provides supporting evidence that the dominant photodetachment channel in TiO- arises from electron emission of the highest ocuupied 9sigma molecular orbital. This provides an immediate assignment of the ground electronic state of TiO- as the doublet 2Delta 3/2 configuration. Similarly, the ground electronic state of Ni - is 2D5/2 with 4s orbital ejection describing the ground state electron affinity transition. Obtained in Chapter 4 is an improved measurement of the electron affinity of ZrO-, determined to be 1.29(1) eV. This energy arises from the assigned anion to neutral ground state, 1Sigma + ← 2Sigma-, electronic transition. Further indentified are features assigned to the 2Delta 3/2 and 2Delta5/2 electronically excited states of the anion, with the 2Delta3/2 spin orbit component measured to lie ∼ 0.10 eV above the 2Sigma - ground state. The first measurement of the photoelectron binding energy spectrum of Pt-, at a fixed frequency photon energy of 2.33 eV is presented in Chapter 5. Intense signatures in the PAD were observed from the electron affinity transition, 3D3 ← 2D5/2. Other observed electronic transitions accessed the closely coupled first and second excited states, 1D2 and 3F4, of neutral Pt. Several weak intensity features were assigned to excitations stemming from the electronically excited states, 2D3/2 and 2S1/2, of metastable Pt- ions. Chapter 5 also presents the photoelectron image of the isoelectronic diatomic molecule, WC-, acquired at a photon energy of 2.33 eV (532 nm). Several electronic transitions originating from the 2Delta3/2 electronic ground state were observed, and the evaluated electron affinity, defined by the transition 2Delta 1 ← 2Delta3/2, was found to be in good agreement with a previous measurement. However, new assignments were made for transitions stemming from the fine structure 2Delta 5/2 component and higher energy 4Sigma- metastable electronic state of the anion. These spectroscopic designations were found to mirror those in the isoelectronic element, Pt- both in energetic term level ordering and total angular momentum symmetry of the occupied molecular orbitals. Discussed in Chapter 6 are the photoelectron imaging experiments conducted on small silicon cluster anions, Sin- (n = 2--7), acquired at a photon energy of 3.49 eV (355 nm). Electronic transitions arising from the anion ground states are assigned, and the evaluated vertical detachment energies are observed to agree well with previous measurements. The anisotropy beta parameters have also been determined for each unique feature appearing in the PADs at the photon energy employed. Presented in Chapter 7 are the results of a high-resolution time-of-flight mass spectrometric study on large silicon hydride cluster anions, Si nHx- (where n = 8--12, 0 ≤ x ≤ 25). The relative abundances of the majority isotopes constituting a precise mass were completely analyzed allowing quantitative assessments of the relative stability for a particular SinHx - cluster to be ascertained. The SinH x- clusters are observed to possess varying stabilities depending on the extent of hydrogenation and the number of silicon atoms constituting the cluster. These trends, and several others, are interpreted with the aid of available theoretical density functional calculations, suggesting geometrical distortions create energetic stabilizations by removing the degeneracy associated with partially filled electronic states. (Abstract shortened by UMI.).
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