A near ultraviolet transition of Mg2F has been observed in emission from the reaction between magnesium clusters, most likely Mg3, and fluorine atoms. Because there is little evidence for upper-state internal excitation, the spectrum is assigned assuming that the upper state is quenched to its lowest vibrational levels. Two of possibly three ground-state vibrational frequencies, υ1 = 516 ± 10 cm-1 and υ2 = 104 ± 10 cm-1, have been established. Dispersed laser-induced fluorescence studies extrapolating on the observed chemiluminescence indicate an excited-state symmetric stretch frequency of order 370 ± 30 cm-1. Electronic structure calculations at the CCSD(T)/CBS level predict that the ground state of Mg2F has C2v symmetry and can be described as an Mg2+F- ion pair with two Mg-F bonds. Like the MgF A-X transition that is largely a transition between Mg orbitals, the observed transition in Mg2F is largely between orbitals on the magnesium dimer ion. The asymmetric C∞v Mg2+F- complex is also a minimum and is predicted to be 6.7 kcal/mol higher in energy. Calculated structures for the Mg2Cl isomers are also presented and used to further interpret the experimental results for the reaction of Mg clusters with Cl atoms. In contrast to Mg2F, the ground state of Mg2Cl is a linear C∞v MgMgCl structure with the C2v and D∞h isomers of the MgClMg structure slightly higher in energy.

This article describes an undergraduate laboratory exercise that uses optical spectroscopy to determine the magnitude and the uncertainty of the Boltzmann constant kb. The more accurate approach uses photoacoustic spectroscopy to measure the Doppler-broadened line profile of individual spectral lines of N2O to extract kb. Measurements and estimates of the uncertainties in the quantities needed to calculate kb from the line profiles are then used to estimate the uncertainty in kb. This experiment is unusual in that it uses advanced laser-based spectroscopy techniques to emphasize standard practices of uncertainty analysis. The core instrumentation is modular and relatively affordable; it requires a tunable single-mode laser, photoreceiver, optical cell, and vacuum pump. If this instrumentation is not available, an alternate approach can be performed which uses the intensity of each rotational transition of an infrared band to measure kb. Although there is more uncertainty using the alternate approach, low concentrations of CO2, DCl, or N2O give reasonable results for the magnitude of kb. Student assessment results indicate retention and mastery of the concept of combined measurement uncertainty.

CrH and CrD molecules have been trapped in solid argon at 4 °K. Infrared spectra, when the large anharmonicity is accounted for, yield predicted gas phase vibrational parameters in the ground state ωe =1615 cm−1 and ωexe=17 cm−1. ESR spectra clearly establish that the molecule has a 6Σ ground state with zero-field-splitting ‖D‖=0.34(1) cm−1 in solid argon and approximate hyperfine coupling constants ‖A (H) ‖=49(5) MHz, ‖A⊥(53Cr) ‖=53(5) MHz, and g⊥?g∥=ge. Several ’’extra lines’’ (off-principal-axis absorptions) in the ESR support the assignment. CrH2 (and CrD2, CrHD) was observed in the IR spectra and may also have been detected in the ESR, which tentatively suggest a S=2 molecule with ‖D‖?0.02 cm−1.

MnH and MnH2 molecules, and their deuterated counterparts, have been trapped in argon and neon matrices at 4 °K and observed via infrared, visible, and electron-spin-resonance spectrscopy. The data for MnH support the gas-phase 7Σ ground-state assignment and yield the magnetic parameters ‖A (H) ‖?20, ‖A∥(Mn) ‖=322(6), ‖A⊥(Mn) ‖=299(2) MHz, g⊥=2.001(1) (assuming g∥ =ge), D=−0.002(1) cm−1. The derived MO description is in essential agreement with the ab initio calculations of Bagus and Schaefer. Infrared data indicate that MnH2 is bent at a bond angle of 117±30°, and stretching force constants are derived. ESR spectra variations with the matrix used and with isotopic substitution indicate motional effects in some matrices. It is concluded that the ground state is 6A1 with ‖D‖=0.20(2) cm−1 and with the probable hyperfine parameters ‖A (H) ‖=36, ‖Axy(Mn) ‖ =73 MHz, where xy is an average axis perpendicular to the H–H direction. The bent molecule is justified by Walsh-type theory applied to transition-metal dihydrides. There are indications that the MnH3 molecule may have also been observed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron spin resonance of the ytterbium fluoride molecule at 4 KR. J. Van Zee, M. L. Seely, T. C. DeVore, and W. Weltner Jr.Cite this: J. Phys. Chem. 1978, 82, 10, 1192–1194Publication Date (Print):May 1, 1978Publication History Published online1 May 2002Published inissue 1 May 1978https://pubs.acs.org/doi/10.1021/j100499a022https://doi.org/10.1021/j100499a022research-articleACS PublicationsRequest reuse permissionsArticle Views103Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

ESR spectra of the MnF and MnF2 molecules trapped in neon and argon matrices have been observed at 4°K. MnF was found to have a 7Σ ground state with the following magnetic parameters in solid neon (assuming g∥=2.002): g⊥=1.999(1), ‖D‖=−0.0107(1) cm−1, ‖A∥(Mn) ‖=490(5), ‖A⊥(Mn) ‖=418(1), ‖A⊥(F) ‖=60(1), and ‖A∥(F) ‖=85(2) MHz. MnF is then highly ionic with the spin density on each F− probably less than about 5%. The Mn+ ion exhibits about 60% of the s character of the free ion. MnF2 is linear with a 6Σg ground state with magnetic parameters in solid neon (assuming g∥=2.002): g⊥=1.994(5), ‖D‖=0.370(3) cm−1, ‖A∥(Mn) ‖=153(6), ‖A⊥(Mn) ‖=124(1), ‖A⊥(F) ‖=19(1) MHz. Comparison of these parameters is made with those obtained earlier from crystalline MnF2 and similar magnetic crystals.