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In this article, we describe an experiment for the undergraduate physical chemistry laboratory in which students measure the compressibility factor of two gases, helium and carbon dioxide, as a function of pressure at constant temperature. The experimental apparatus is relatively inexpensive to construct and is described and diagrammed in detail. Students analyze their data to determine values for the second virial coefficient for each gas, which may then be compared with the literature. The experiment demonstrates the nonideality of real gases. (Contains 2 tables and 2 figures.)

The acetylperoxy + HO2 reaction has multiple impacts on the troposphere, with a triplet pathway leading to peracetic acid + O2 (reaction (1a)) competing with singlet pathways leading to acetic acid + O3 (reaction (1b)) and acetoxy + OH + O2 (reaction (1c)). A recent experimental study has reported branching fractions for these three pathways (α1a, α1b, and α1c) from 229 K to 294 K. We constructed a theoretical model for predicting α1a, α1b, and α1c using quantum chemical and Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) simulations. Our main quantum chemical method was Weizmann-1 Brueckner Doubles (W1BD) theory; we combined W1BD and equation-of-motion spin-flip coupled cluster (SF) theory to treat open-shell singlet structures. Using RRKM/ME simulations that included all conformers of acetylperoxy–HO2 pre-reactive complexes led to a 298 K triplet rate constant, k1a = 5.11 × 10−12 cm3 per molecule per s, and values of α1a in excellent agreement with experiment. Increasing the energies of all singlet structures by 0.9 kcal mol−1 led to a combined singlet rate constant, k1b+1c = 1.20 × 10−11 cm3 per molecule per s, in good agreement with experiment. However, our predicted variations in α1b and α1c with temperature are not nearly as large as those measured, perhaps due to the inadequacy of SF theory in treating the transition structures controlling acetic acid + O3 formation vs. acetoxy + OH + O2 formation. [ABSTRACT FROM AUTHOR]

Quantum chemistry and RRKM/master equation calculations are used to characterize the effect of the vinyl group on the chemistry of the methyl vinyl carbonyl oxide. Natural bond order analysis revealed that the vinyl group weakens the C=O bond of the carbonyl oxide, also dioxole formation, which has a CBS-QB3 reaction barrier of 13.9 kcal/mol, and it is found to be favored over vinyl hydroperoxide formation, dioxirane formation, and collisional stabilization.

Investigate on the computational evidence against the mechanism of alpha-hydroxycarbonyl formation is done. In the conclusion the master equation simulations are necessary to quantify the extent to which carboxylic acids from anti carbonyl oxides also contributes to HO(sub x) production in ozonolysis.

The mechanism of the ene reaction of singlet ((super 1)Delta(sub g) oxygen with simple alkenes is investigated by a combination of experimental isotope effects and several level of theoretical calculations. The result provides the first experimental support for a reaction surface involving two adjacent transition states.

A variation on the themes of thermally accessible excited states and state selectivity is reported. From the spectroscopic observations of certain N=O stretching frequencies in argon-matrix-isolation products from the reaction of NO with O2 or (super 18)O(sub 2) are likely from ONONO(sub 2) not the OONO radical.

Research is done on the OH radical which is the key oxidizing agent in the troposphere, and ozone--alkene reactions appear to be a significant and sometimes dominant source of new HO, radicals in urban and rural air. In conclusion, they lead to the proposal that the formation of a hydroperoxide via a diradical pathway can compete with the formation of the carbonyl oxide for the ethene primary ozonide.

The hydrogen-bonded and free OH stretch modes of Cl(super -)(H2O)n (n = 1-5) were investigated by vibrational predissociation spectroscopy in the 1.6-3.2 microns region. Results showed that all clusters produce strong ionic hydrogen bonds and the presence of water-water hydrogen-bonding networks in n = 4 and n = 5, with the wide spectrum of n = 5 similar to that of large neural water clusters. No water-water hydrogen bonding was observed in n = 2 and n = 3, but these clusters seemed to be solvated asymmetrically.

The B 2[uppercase_phi_synonym]5/2-X1 2Δ3/2(0,0) band at 778 nm and the C 2Δ3/2-X1 2Δ3/2(0,0) band at 737 nm of tantalum oxide (TaO) were recorded by laser excitation spectroscopy using a hollow cathode sputtering source to generate the molecules. The hyperfine structure arising from the 181Ta (I=7/2) nucleus was measured at sub-Doppler resolution using the technique of intermodulated fluorescence spectroscopy. The hyperfine structure was assigned and fitted in order to derive accurate values for the magnetic dipole and electric quadrupole interactions. The magnetic hyperfine constant for the ground electronic state was also calculated using the density functional theory as h3/2=625 MHz, in good agreement with the experimental value of 647±10 MHz. This result suggests that the X 2Δ ground state of TaO is well described by a pure δσ2 electronic configuration, where the unpaired electron is located in a Ta 5dδ orbital. [ABSTRACT FROM AUTHOR]

Density functional theory and composite electronic structure methods were used to predict the energetics of intramolecular hydrogen atom transfers in the [beta]-hydroxyethylperoxy and [beta]-hydroxyethoxy radicals. The methods used predict relative stabilities for the conformers of I and III as per the CBS-QB3 composite method if the basis set used in the DFT calculations includes diffuse functions on non-hydrogen atoms.

The parent and substituted vinoxy radicals are key intermediates in both combustion and atmospheric chemistry. Experiment and theory indicate that vinoxy radicals react with moderate facility with molecular oxygen to form alpha-oxoperoxy radicals.

Infrared spectra of mass-selected clusters NO+(H2O)n for n=1 to 5 were recorded from 2700 to 3800 cm-1 by vibrational predissociation spectroscopy. Vibrational frequencies and intensities were also calculated for n=1 and 2 at the second-order Mo\ller–Plesset (MP2) level, to aid in the interpretation of the spectra, and at the singles and doubles coupled cluster (CCSD) level energies of n=1 isomers were computed at the MP2 geometries. The smaller clusters (n=1 to 3) were complexes of H2O ligands bound to a nitrosonium ion NO+ core. They possessed perturbed H2O stretch bands and dissociated by loss of H2O. The H2O antisymmetric stretch was absent in n=1 and gradually increased in intensity with n. In the n=4 clusters, we found evidence for the beginning of a second solvation shell as well as the onset of an intracluster reaction that formed HONO. These clusters exhibited additional weak, broad bands between 3200 and 3400 cm-1 and two new minor photodissociation channels, loss of HONO and loss of two H2O molecules. The reaction appeared to go to completion within the n=5 clusters. The primary dissociation channel was loss of HONO, and seven vibrational bands were observed. From an analysis of the spectrum, we concluded that the n=5 cluster rearranged to form H3O+(H2O)3(HONO), i.e., an adduct of the reaction products. [ABSTRACT FROM AUTHOR]

OH radical formation yields from the reaction of ozone with several cycloalkenes are calculated using small amounts of fast-reacting aromatics and aliphatic ethers to trace OH formation. The results indicate that the OH production from cycloalkalenes is largely controlled by the transition states for the cycloreversion of the primary ozonide.

The atmospheric oxidation of sulfurdioxide by the parent and dimethyl Criegee intermediates (CIs) maybe an important source of sulfuric acid aerosol, which has a largeimpact on radiative forcing and therefore upon climate. A number ofcomputational studies have considered how the CH2OOS(O)Oheteroozonide (HOZ) adduct formed in the CI + SO2reactionconverts SO2to SO3. In this work we use theCBS-QB3 quantum chemical method along with equation-of-motion spin-flipCCSD(dT) and MCG3 theories to reveal new details regarding the formationand decomposition of the endoand exoconformers of the HOZ. Although ∼75% of the parent CI + SO2reaction is initiated by formation of the exoHOZ, hyperconjugation preferentially stabilizes many of the endointermediates and transition structures by 1–5kcal mol–1. Our quantum chemical calculations, inconjunction with statistical rate theory models, predict a rate coefficientfor the parent CI + SO2reaction of 3.68 × 10–11cm3molecule–1s–1, in good agreement with recent experimental measurements.RRKM/master equation simulations based on our quantum chemical datapredict a prompt carbonyl + SO3yield of >95% for thereaction of both the parent and dimethyl CI with SO2. Theexistence of concerted cycloreversion transition structures 10–15kcal mol–1higher in energy than the HOZ accountsfor most of the predicted SO3formation. [ABSTRACT FROM AUTHOR]