On the vibronic level structure in the NO_3 radical. Part III. Observation of intensity borrowing via ground state mixing

The A^2E" ← X^2A'_2 absorption spectrum exhibits vibronically allowed transitions from the ground state of NO_3 to upper state levels having a"_1 and e' vibronic symmetries. This paper explores the coupling mechanisms that lend intensities to these features. While transitions to e' vibronic levels borrow intensity from the very strong B^2E' ← X^2A'_2 electronic transition, those to a"_1 levels involve only negligible upper-state borrowing effects. Rather, it is the vibronic mixing of the ground vibronic level of NO_3 with vibrational levels in the B^2E' electronic state that permit the a"_1 levels to be seen in the spectrum. These ideas are supported by vibronic coupling calculations. The fact that the intensities of features corresponding to the two different vibronic symmetries are comparable is thus accidental

IL9. Thermochemistry: Not as Boring as You Might Think

Developed during the last decade by Ruscic and collaborators at Argonne National Laboratory, Active Thermochemical Tables (ATcT) represents an entirely new and revolutionary way to approach the subject of thermochemistry. Traditional thermochemistry has advanced piecemeal and willy nilly, through individual spectroscopic, kinetic, calorimetric, etc. mea-surements often supplemented by \u27recommendation of \u27standard (in the non-thermodynamic sense) through the actions of various critical review committees (NIST-JANAF, CODATA, etc.). In contrast, ATcT is a holistic approach that views each molecule as connected in principle to all other species through within constructs called thermochemical networks. In ATcT, thermochemical parameters such as bond energies, ionization potentials, and en-thalpies of formation are solved for self-consistently using all available relevant information. Many bond energies once known to, say, a few kcal mol-1 have now been established with aprecisionthatis atleastanorderofmagnitudebetterthan before, whichclearlyhas enormous practical consequences for modelling studies. This talk reviews the surprisingly interesting topic of where do these heats of formation come from? and outlines the basic ideas in ATcT. Due to the high interconnectedness of many chemical species through the thermochemical network paradigm, it transpires that knowing any individual property (say, an ionization potential) can potentially impact properties of any number of different species. Hence, there is virtue to constantly improving our knowledge of fundamental molecular prop-erties that goes well beyond just putting another decimal place on it. ATcT actively seeks accurate measurements and calculations for key quantities, which will be illustrated by a recent study of the photoelectron spectrum of hydrogen peroxide

New insights into the Jahn–Teller effect in NO_3 via the dark à 2E" state

The recent cavity ringdown (CRD) measurement of the forbidden Ã^2 E"←X~^2 A2' transition of the nitrate radical NO_3 reveals a rich, well-resolved spectrum in the near-infrared. The spectroscopic detail provides a new window onto the Jahn–Teller (JT) and pseudo-Jahn–Teller (PJT) effects in NO_3. This paper reviews the current experimental evidence for vibronic coupling in the à state and discusses the theoretical issues in the context of new preliminary EOMIP/CCSD and CCSD(T) calculations. The theoretical results to date indicate that the à 2E" state of NO_3 undergoes a relatively strong JT distortion which may require inclusion of higher order vibronic couplings. The intensity of this transition may involve multiple intensity borrowing mechanisms via PJT coupling among the X~, à and B~ states

The Relative Importance of Search versus Credence Product Attributes: Organic and Locally Grown

Organic foods and local foods have come to the forefront of consumer issues, due to concerns about nutrition, health, sustainability, and food safety. A conjoint analysis experiment quantified the relative importance of, and trade-offs between, apple search and experience attributes (quality/blemishes, size, flavor), credence attributes (conventional vs. organic production method, local origin vs. product of USA vs. imported), and purchase price when buying apples. Quality is the most important apple attribute. Production method—organic versus conventional—had no significant impact on preferences.conjoint analysis, organic, locally grown, credence attributes, Consumer/Household Economics, Food Consumption/Nutrition/Food Safety, Marketing,

Electron diffraction studies of hot molecules. IV. Asymmetries of nonbonded distribution functions of SF6, SiF4, and CF4

Highly significant improvements in the agreement between observed and calculated intensities of electrons diffracted by hot molecules were obtained by optimizing the skew parameter â for the nonbonded distributions. Derived â values (±2σ) were 2.75(11), 0.72(13), and 2.0(4) Å−1 for SF6, SiF4, and CF4, respectively. These measured skew parameters are approximately 2 Å−1 higher in each case than values previously proposed on the basis of Morse asymmetry factors and the nonlinear transformation between curvilinear and normal coordinates of molecules. The principal factor responsible for the increase is the previously unknown intrinsic anharmonicity in bending deformations. Silicon tetrafluoride has a lower â value than the other molecules studied primarily because its bending force constant is lower, relative to stretching. Practical as well as theoretical implications of present findings are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70475/2/JCPSA6-81-9-3792-1.pd

Theoretical prediction of magnetic exchange coupling constants from broken-symmetry coupled cluster calculations

Exchange coupling constants (J) are fundamental to the understanding of spin spectra of magnetic systems. Here, we investigate the broken-symmetry (BS) approaches of Noodleman and Yamaguchi in conjunction with coupled cluster (CC) methods to obtain exchange couplings. J values calculated from CC in this fashion converge smoothly toward the full configuration interaction result with increasing level of CC excitation. We compare this BS-CC scheme to the complementary equation-of-motion CC approach on a selection of bridged molecular cases and give results from a few other methodologies for context

LOW-LYING ELECTRONIC STATES OF C4H: NOT SIMPLE

The C$_4$H molecule is of significant astronomical interest. It represents one of the smallest ``carbon chain” radicals, is abundantly distributed in astronomical sources, and C$_4$H$^-$ was the one of the first molecular anions to be detected in space. The acetylenic radicals H(C$_2$)$_n$ form an interesting sequence in which low-lying excited electronic states are conspicuous. The simplest radical (C$_2$H) has a $^2\Sigma$ ground state, with the $^2\Pi$ excited state just below 0.5 eV higher. As the length of the carbon chain increases, the delocalization present in the $^2\Pi$ state (relative to $^2\Sigma$, which is acetylenic in nature with the unpaired spin localized on the terminal carbon) leads to its preferential stabilization, and $^2\Pi$ lies comfortably below $^2\Sigma$ for C$_6$H and larger members of the series. In this regard, C$_4$H sits essentially on the frontier: the most recent experiments place the $^2\Sigma$ lowest, but by only $<$30 meV, and a clear picture of its low-level vibronic level structure has yet to emerge. This talk discusses all three of the low-lying states ($^2\Sigma$ and the two components of $^2\Pi$), which in fact display a low-lying three-state conical intersection within 150 meV of the minimum on the adiabatic surface, and undergo profound vibronic pseudo-Jahn-Teller ($^2\Sigma$/$^2\Pi$) and Renner-Teller ($^2\Pi$) mixing. High-level calculations are performed to identify the various principal stationary points and conical intersections on the potential, and this information is used to construct a three-state vibronic Hamiltonian of the Köppel-Cederbaum-Domcke variety. These results are used to present a view of the electronic structure of this molecule that goes beyond the simple description of simple $^2\Sigma$ and Renner-Teller distorted $^2\Pi$ states that has typically been invoked in the past, and to carry out a simulation of the photoelectron spectrum.