Three new infrared bands of the He-OCS complex

Three new infrared bands of the weakly-bound He-OCS complex are studied, using tunable lasers to probe a pulsed supersonic slit jet expansion. They correspond to the (0400) <-- (0000), (1001)<-- (0000), and (0401) <-- (0000) transitions of OCS at 2105, 2918, and 2937 cm-1, respectively. The latter band is about 7900 times weaker than the previously studied OCS nu1 fundamental. Vibrational shifts relative to the free OCS monomer are found to be additive. Since carbonyl sulfide has previously been shown to be a valuable probe of superfluid quantum solvation effects in helium clusters and droplets, the present results could be useful for future studies of vibrational effects in such systems.Comment: 16 pages, 1 figure, 4 table

Systematic experimental comparison of particle filtration efficiency test methods for commercial respirators and face masks

Respirators, medical masks, and barrier face coverings all filter airborne particles using similar physical principles. However, they are tested for certification using a variety of standardized test methods, creating challenges for the comparison of differently certified products. We have performed systematic experiments to quantify and understand the differences between standardized test methods for N95 respirators (NIOSH TEB-APR-STP-0059 under US 42 CFR 84), medical face masks (ASTM F2299/F2100), and COVID-19-related barrier face coverings (ASTM F3502-21). Our experiments demonstrate the role of face velocity, particle properties (mean size, size variability, electric charge, density, and shape), measurement techniques, and environmental preconditioning. The measured filtration efficiency was most sensitive to changes in face velocity and particle charge. Relative to the NIOSH method, users of the ASTM F2299/F2100 method have commonly used non-neutralized (highly charged) aerosols as well as smaller face velocities, each of which may result in approximately 10% higher measured filtration efficiencies. In the NIOSH method, environmental conditioning at elevated humidity increased filtration efficiency in some commercial samples while decreasing it in others, indicating that measurement should be performed both with and without conditioning. More generally, our results provide an experimental basis for the comparison of respirators certified under various international methods, including FFP2, KN95, P2, Korea 1st Class, and DS2.Comment: 34 pages, 8 figures, 3 table

Observation of a planar isomer of the OCS-(C2H2) 2 trimer

Infrared spectra of a new planar isomer of the OCS-(C2H 2)2 trimer are observed in the region of the OCS \u3bd1 fundamental band ( 3c2060 cm-1) using a tunable diode laser to probe a pulsed supersonic slit jet expansion. Three isotopologues are analyzed in detail (16OCS-(HCCH)2, 16OCS-(DCCD)2, and 18OCS-(DCCD)2), while the spectrum of a fourth is found to be heavily perturbed ( 18OCS-(HCCH)2). Observed rotational constants of planar OCS-(C2H2)2 agree fairly well with previous ab initio calculations, and with previous and present semi-empirical calculations. It should now be possible to assign the microwave spectrum of planar OCS-(C 2H2)2. \ua9 2011 Elsevier B.V. All rights reserved.Peer reviewed: YesNRC publication: Ye

INFRARED SPECTRA OF He--CS2_2, Ne--CS2_2, AND Ar--CS2_2

Author Institution: Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N; 1N4, CanadaInfrared spectra of weakly bound Rg--CS$_2$ (Rg = He, Ne, and Ar) clusters formed in a pulsed supersonic slit-jet expansion have been recorded by exciting the CS$_2$ $\nu_3$ fundamental band ($\sim$ 1535 cm$^{-1}$) using a tuneable diode laser. Spectra were well fitted to a conventional semi-rigid asymmetric rotor Hamiltonian. The He--CS$_2$ spectrum was assigned to an a-type band, while spectra of Ne--CS$_2$ and Ar--CS$_2$ were well described by b-type bands, indicating a/b axis switching in transition from the He--CS$_2$ complex to the Ne--CS$_2$ and Ar--CS$_2$ complexes. The results show that the complexes have vibrationally averged T-shaped structures. The determined structural parameters along with the observed vibrational shifts are $R=3.81, 3.57$ and $3.71$ {\AA}, $\theta = 80.0, 86.9$ and 86.4^irc} and $\Delta\nu = 0.171, 0.181$ and $0.067$ cm$^{-1}$ for He--CS$_2$, Ne--CS$_2$ and Ar--CS$_2$, respectively. Here, $R$ is the distance between the rare gas and the carbon atom, $\theta$ is the the angle between $R$ and and the CS$_2$ axis and $\Delta\nu$ is the vibrational shift with respect to the free CS$_2$ monomer

Spectroscopic observation and structure of CS2 dimer

Infrared spectra of the CS2 dimer are observed in the region of the CS2 \u3bd3 fundamental band ( 3c1535 cm-1) using a tunable diode laser spectrometer. The weakly bound complex is formed in a pulsed supersonic slit-jet expansion of a dilute gas mixture of carbon disulfide in helium. Contrary to the planar slipped-parallel geometry previously observed for (CO2)2, (N2O)2, and (OCS)2, the CS2 dimer exhibits a cross-shaped structure with D2d symmetry. Two bands were observed and analyzed: the fundamental (C-S asymmetric stretch) and a combination involving this mode plus an intermolecular vibration. In both cases, the rotational structure corresponds to a perpendicular (\u394K = \ub11) band of a symmetric rotor molecule. The intermolecular center of mass separation (C-C distance) is determined to be 3.539(7) \uc5. Thanks to symmetry, this is the only parameter required to characterize the structure, if the monomer geometry is assumed to remain unchanged in the dimer. From the band centers of the fundamental and combination band an intermolecular frequency of 10.96 cm-1 is obtained, which we assign as the torsional bending mode. This constitutes the first high resolution spectroscopic investigation of CS2 dimer. \ua9 2011 American Institute of Physics.Peer reviewed: YesNRC publication: Ye

High resolution infrared spectroscopy of carbon dioxide clusters up to (CO 2) 13

Thirteen specific infrared bands in the 2350 cm -1 region are assigned to carbon dioxide clusters, (CO 2) N, with N = 6, 7, 9, 10, 11, 12 and 13. The spectra are observed in direct absorption using a tuneable infrared laser to probe a pulsed supersonic jet expansion of a dilute mixture of CO 2 in He carrier gas. Assignments are aided by cluster structure calculations made using two reliable CO 2 intermolecular potential functions. For (CO 2) 6, two highly symmetric isomers are observed, one with S 6 symmetry (probably the more stable form), and the other with S 4 symmetry. (CO 2) 13 is also symmetric (S 6), but the remaining clusters are asymmetric tops with no symmetry elements. The observed rotational constants tend to be slightly ( 482%) smaller than those from the predicted structures. The bands have increasing vibrational blueshifts with increasing cluster size, similar to those predicted by the resonant dipole-dipole interaction model but significantly larger in magnitude. \ua9 2011 American Institute of Physics.Peer reviewed: YesNRC publication: Ye

New spectroscopic results on acetylene dimers and trimers

Spectra of acetylene dimers and trimers containing one or more C2D2 monomer are studied in the \u3bd3 fundamental band region of C2D2 ( 482440\u2009cm 12\ub9) using a tuneable infrared diode laser to probe a pulsed supersonic slit jet expansion. Four new subbands are observed in the perpendicular band of (C2D2)2, and this enables the first direct determination of the A rotational constant for an acetylene dimer. The value found for A is significantly larger than the previous indirect value based on microwave spectra. The dimer parallel band is observed and found to be highly perturbed, and observations are extended for the mixed dimer C2D2 \u2013 C2H2. The trimers (C2D2)3, (C2D2)2 \u2013 C2H2, and C2D2 \u2013 (C2H2)2 are observed spectroscopically for the first time. Establishment of a precise band origin is difficult for (C2D2)3 because of the inherent nature of the spectrum, but this is possible for two out of three of the bands of the mixed trimers.Peer reviewed: YesNRC publication: Ye

INFRARED SPECTRUM OF THE (CO2)2_2)_2-N2_2O TRIMER MEASURED IN N2_2O ν1\nu_1 AND ν3\nu_3 REGIONS.

Author Institution: Department of Physics and Astronomy, University of Calgary, 2500 University Dr., N.W., Calgary, Alberta T2N 1N4, Canada; National Research Council of Canada, Ottawa, Ontario, K1A 0R6, CanadaInfrared spectra of the (CO$_2)_2$-N$_2$O trimer are observed by exciting the $\nu_1$ and $\nu_3$ fundamental stretching vibrations of the N$_2$O moiety (around 1285 cm$^{-1}$ and 2224 cm$^{-1}$ respectively). Spectra are recorded using a pulsed supersonic jet apparatus with a tunable diode laser probe. Ground state parameters were previously determined from a microwave study. \textbf{96}, 1355 (1999).} Analysis of the infrared spectra reveals information on the vibrational shifts upon complex formation as well as molecular parameters for the excited states. Our cluster calculation program yields a minimum energy structure very similar to that from the Orient program\textsuperscript{\textit{a}} but in slightly better agreement with the experimental structure. Our cluster calculations indicate a close resemblance of the two lowest energy isomers to those of (CO$_2$)$_2$-OCS