Spectroscopy and electronic structure of jet-cooled GaAs

Journal ArticleAn optical spectrum, obtained by resonant two-photon ionization spectroscopy, is reported for jet-cooled diatomic gallium arsenide. The ground state is identified as X??-, deriving from a ??rr? molecular configuration, and is characterized by ?" = 215 cm-1, ?"exe" = 3 cm-1, and r0' = 2.53 ? 0.02 ?. The upper state of the observed band system is 3IIr correlating to the Ga 4s?4p, ?P? + As 4s?4p?, ?D0 excited separated atom limit. A strong predissociation sets in above v'=0 for the ?'=2,1 and 0- components of the 3IIr excited state, and it is proposed that this is induced by spin-orbit interaction with the ??*rr?,??- state which correlates to ground state atomic fragments. Constants for the upper ?IIo+ state are ?'e = 152.13 ? 0.70 cm-1, ?'ex'e = 2.89 ? 0.08 cm-1, and r"e = 2.662 ? 0.027 A for the 69Ga7 5As isotopic modification. The ionization potential of GaAs has been bracketed as IP(GaAs) = 7.17 ? 0.75 eV, and a reevaluation of the third-law measurement of the bond strength provides D0(GaAs) = 2.06 ? 0.05 eV. Comparisons to group IV and other group HI-V diatomics, and to the bulk solid materials are also presented

A pair potentials study of matrix-isolated atomic zinc. II. Intersystem crossing in rare-gas clusters and matrices

Journal ArticleThe mechanism of 4p 1P1?4p 3PJ intersystem crossing (ISC) following excitation of the 4p 1P1 level of matrix-isolated atomic zinc is investigated using a pair potentials approach. This is achieved by extending earlier ISC calculations on the Zn?RG2 and Zn?RG3 complexes to the square planar Zn?RG4 and square pyramidal Zn?RG5 species which are the building blocks of the Zn?RG18 cluster used to represent the isolation of atomic zinc in the substitutional site of a solid rare-gas host. ISC predictions in these clusters are based on whether crossing of the strongly bound 1A1 states, having a 4p 1P1 atomic asymptote, occurs with the repulsive 3E states correlating with the 4p 3PJ atomic level of atomic zinc. Predictions based on 1A1 /3E curve crossings for 3E states generated with the calculated ab initio points for the Zn?RG 3S(pz) states do not agree with matrix observations. Based on similar overestimation of ISC in the Zn?RG diatomics, less repulsive Zn?RG 3S(pz) potential curves are used resulting in excellent agreement between theory and observations in the Zn?RG matrix systems. 1A1 /3E curve crossings do not occur in the Zn?Ar system which shows only singlet emission. Curve crossings are found for the Zn?Xe system which exhibits only triplet emission. The Zn?Kr system does not show a crossing of the body mode Q2 , which exhibits a strong singlet emission at 258 nm while the waist mode Q3 , does have a crossing, resulting in a weak singlet emission at 239 nm and a stronger triplet emission at 312 nm. The efficiency of ISC is determined from Landau?Zener estimates of the surface hopping probabilities between the 1A1 and the 3E states. Differences in the application of this theory in the gas and solid phase are highlighted, indicating that the rapid dissipation of the excited-state energy which occurs in the solid must be included to obtain agreement with observations

Renormalized One-loop Theory of Correlations in Disordered Diblock Copolymers

A renormalized one-loop theory (ROL) is used to calculate corrections to the random phase approximation (RPA) for the structure factor \Sc(q) in disordered diblock copolymer melts. Predictions are given for the peak intensity $S(q^{\star})$, peak position $q^{\star}$, and single-chain statistics for symmetric and asymmetric copolymers as functions of $\chi N$, where $\chi$ is the Flory-Huggins interaction parameter and $N$ is the degree of polymerization. The ROL and Fredrickson-Helfand (FH) theories are found to yield asymptotically equivalent results for the dependence of the peak intensity $S(q^{\star})$ upon $\chi N$ for symmetric diblock copolymers in the limit of strong scattering, or large $\chi N$, but yield qualitatively different predictions for symmetric copolymers far from the ODT and for asymmetric copolymers. The ROL theory predicts a suppression of $S(q^\star)$ and a decrease of $q^{\star}$ for large values of $\chi N$, relative to the RPA predictions, but an enhancement of $S(q^{\star})$ and an increase in $q^{\star}$ for small $\chi N$ ($\chi N < 5$). By separating intra- and inter-molecular contributions to $S^{-1}(q)$, we show that the decrease in $q^{\star}$ near the ODT is caused by the $q$ dependence of the intermolecular direct correlation function, and is unrelated to any change in single-chain statistics, but that the increase in $q^{\star}$ at small values of $\chi N$ is a result of non-Gaussian single-chain statistics.Comment: 16 pages, 13 figures, submitted to J. Chem. Phy