[1] We present a kinetic calculation for the isotopic composition of stratospheric ozone. The calculated enrichments of 49 O 3 and 50 O 3 are in agreement with atmospheric measurements made at midlatitudes. Integrating the kinetic fractionation processes in the formation and photolysis of ozone, we obtain enrichments of $7.5-10.5 and $7.5-12.5% (referenced to atmospheric O 2 ) for d O 3 and d50 O 3 , respectively, at altitudes between 20 and 35 km; the photolysis in the Hartley band of ozone is responsible for the observed altitude variation. The overall magnitude of the ozone enrichments ($10%) is large compared with that commonly known in atmospheric chemistry and geochemistry. The heavy oxygen atom in ozone is therefore useful as a tracer of chemical species and pathways that involve ozone or its derived products. For example, the mass anomalies of oxygen in two greenhouse gases, CO 2 and N 2 O, are likely the consequences of the transfer of heavy oxygen atoms from ozone.

[1] In the photodissociation of N 2 O, absorption cross sections differ with isotopic substitution, leading to a wavelength-dependent fractionation of the various isotopomers. Several models ranging from shifts by zero-point energy differences to propagation of wave packets on the excited electronic state potential energy surface have been proposed to explain the observed fractionations. We present time-independent fractionation calculations for the isotopomers 447, 448, 456, 546, and 556. Besides largely agreeing with the experimental data, these calculations have the advantage of not being computationally intensive, as well as satisfying the physical facts that the asymmetric stretch and the doubly degenerate bending vibration are the principal Franck-Condon active modes in the photodissociation. The latter is reflected in the actual dissociation and in the high rotational excitation and lack of vibrational excitation of the N 2 product. The calculations are based on a multidimensional reflection principle using an ab initio potential energy surface. The theory for the absorption cross section and isotopomer fractionation accompanying photodissociation is described. The absolute value of the theoretically calculated absorption cross section is very close (90%) to the experimentally observed value. The present computations also provide data for the slope of a threeisotope plot of the fractionation of 447/446 relative to 448/446, using the fractionations at different wavelengths. The resulting slope is compared with a perturbation theoretical expression for direct photodissociation given elsewhere.

The effect of weak interactions on the ring puckering potential in the coumaran-argon van der Waals complex: Experimental and ab initio analysis of the intermolecular and low-frequency intramolecular vibrations Ab initio determination of the far infrared spectra of some isotopic varieties of ethanolThe intracavity dye laser photoacoustic absorption spectra of ethanol, ethanol (1,1-d 2 ), and ethanol (2,2,2-d 3 ) are reported for the region 16 550-16 700 cm Ϫ1 , which contains the O-H fourth overtone (⌬ OH ϭ5) vibration. The distinct absorption bands have been assigned to the trans and gauche conformational isomers. Comparison of the spectra reveals a coupling between the OH and methylene CH vibrations in only the gauche conformer of ethanol, an effect that had not been observed in the fundamental spectrum. Ab initio electronic structure and vibrational frequency calculations are used to clarify and support the analysis of the ethanol OH vibrational spectrum and to evaluate the relative energies of the conformers.

Articles you may be interested inStudy of linear and nonlinear optical properties of dendrimers using density matrix renormalization group method J. Chem. Phys. 131, 074111 (2009); 10.1063/1.3202437 Quantum-chemical investigation of second-order nonlinear optical chromophores: Comparison of strong nitrilebased acceptor end groups and role of auxiliary donors and acceptorsThe equivalent internal field model, originally developed for linear one-dimensional chromophores, is extended to three-dimensional multipolar chromophores. The extension requires two generalizations to the model. First, the equivalent internal field must be generalized to an equivalent internal potential. Second, all tensor components of the hyperpolarizability must be taken into account. A general formalism is developed for analyzing the hyperpolarizabilities induced by application of various internal potentials to a molecular skeleton, assuming the hyperpolarizabilities are linearly related to the internal potential. This formalism utilizes a symmetry analysis, along with quantum chemical calculations done here with the Hückel, Pariser-Parr-Pople and intermediate neglect of differential overlap ͑INDO͒ Hamiltonians and using single-configuration interaction theory. The formalism is applied to and tested on the benzene molecular skeleton. The hyperpolarizability is found to be linearly related to the internal potential provided the potential difference between carbon atoms is below a threshold of the order of 2 eV. Various predictions of the model are tested against explicit INDO and ab initio calculations on mono-substituted, ortho-disubstituted, meta-disubstituted, and tri-substituted benzenes. For the substituents F, CH 3 , OCH 3 , OH, and NH 2 , many of the predictions of the equivalent internal potential model apply, indicating that the internal potentials arising from these substituents are in the linear regime. For the NO 2 and CN substituents, strong effects from nonlinear coupling are observed. The disagreements between the various quantum chemical treatments ͑INDO and various ab initio approaches͒ are largest for molecules exhibiting nonlinear coupling effects, indicating that the nonlinear effects are more difficult to calculate than linear effects. , ͑21͒where the sum is over all J and M . Due to Kleinmann symmetry, 5,7 which is valid away from resonance, only the Jϭ1 and Jϭ3 components are nonzero.

The use of electronic formats for obtaining, recording, analyzing, and disseminating data is becoming ubiquitous in classrooms, teaching laboratories, research laboratories, and industry. The undergraduate physical chemistry teaching laboratory provides an excellent opportunity to ensure that upper-division chemistry students gain experience in using electronic means of recording and presenting the results of their experiments. To facilitate this action, computers are used in as many aspects of the course as possible: obtaining introductory material, preparing pre-lab reports, recording data in a simulated electronic lab notebook, and submitting final lab reports. Since the physical chemistry laboratory is an advanced undergraduate course, the students are also given increased responsibility for the experiment, creating their own procedure from papers, textbooks, and other additional information.