Integrating Physical Principles with Machine Learning for Predicting Field-Enhanced Catalysis
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Quantitative validation of Ames IR intensity and new line lists for (32/33/34)S(16)O2, (32)S(18)O2 and (16)O(32)S(18)O
The quality of Ames-296K SO2 Infrared (IR) line list intensities is first validated by quantitative exploration of several dipole moment surfaces (DMSs) and partition sum convergence. The DMSs are computed with several of Dunning’s correlation-consistent basis sets and their vibrational dependence are compared to the empirical model derived from Stark effect experiments reported by D. Patel, D. Margolese, and T.R. Dykea [J.Chem.Phys. 70, 2740 (1979)]. The effective dipole deviations from the DMS adopted in the Ames IR lists is 0.2-0.4% for vibrational states up to 3v3. The vibrational dependence of the dipole moment is also in good agreement, except for nv1. Partition sum convergence at 296K is confirmed by new calculations with rotational quantum number J up to 150 and upper state E’ up to 8000 cm-1. The isotopologue consistency of the Ames IR line lists is superior relative to the regular Effective Hamiltonian (EH) models and Effective Dipole Moment (EDM) models. The v1+v2 and v2+v3 intensity consistency check reveals the recently reported experimental intensities need significant improvement or re-analysis. After the accuracy, convergence, and isotopologue consistency have been confirmed, the theoretical Ames-296K intensities are combined with the experimental line positions or EH models that experimental spectroscopists published after 2009. Three high-resolution IR line sets are reported for the (32/33/34)S(16)O2, (32)S(18)O2 and (16)O(32)S(18)O isotopologues: (1) the “New Lines Sets” include experimentally measured line positions; (2) the “Expanded Line Sets” include possible transitions among new rovibrational levels assigned in experiments and ground state (GS) levels predicted by reliable EH models; (3) the “Ames + MARVEL Sets” include possible transitions among all those levels reported in a recent MARVEL analysis. [Tóbiás et al, JQSRT 208, 152 (2018)]. Compared to the limited data in High-resolution TRANsmission molecular absorption database (HITRAN), these line sets have significantly improved the data coverage up to 4000 cm-1. Some missing bands can be traced to the unpublished experimental data. The isotopologue consistency of these line sets will help identify the uncertainties and defects in the experimental EH and EDM models. These line sets are good candidates for the next HITRAN update, if line shape parameters are available. The line sets can be downloaded from supplementary files or from the Ames Molecular Spectroscopic Database at http://huang.seti.org.
Xinchuan Huang↗
Tunable Far Infrared Studies in Support of Stratospheric Measurements
This report summarizes research done under NASA Grant NAG5-4653. The research performed under this grant has been a collaboration between institutions including the Smithsonian Astrophysical Observatory, the National Institute of Standards and Technology, the University of Oregon, and the NASA Langley Research Center. The program has included fully line-resolved measurements of submillimeter and far infrared spectroscopic line parameters (pressure broadening coefficients and their temperature dependences, and line positions) for the analysis of field measurements of stratospheric constituents, far infrared database improvements, and studies for improved satellite measurements of the Earth's atmosphere. This research program is designed to enable the full utilization of spectra obtained in far infrared/submillimeter field measurements, such as FIRS-2, FILOS, IBEX, SLS, EosMLS, and proposed European Space Agency measurements of OH (e.g., PIRAMHYD and SFINX) for the retrieval of accurate stratospheric altitude profiles of key trace gases involved in ozone layer photochemistry. For the analysis of the spectra obtained in the stratosphere from far infrared measurements it is necessary to have accurate values of the molecular parameters (line positions, strengths, and pressure broadening coefficients) for the measured molecules and for possible interfering species. Knowledge of line positions is in increasingly good shape, with some notable exceptions. The increase in position information includes research that has been performed in the present program of research on HO2, H2O, H2O2, O3, HCl, HF, HBr, HI, CO, OH, and ClO. Examples where further line position studies are necessary include hot band and minor isotopomer lines of some of the major trace species (H2O, O3) and normal lines of some triatomic and larger molecules (NO2). Knowledge of strengths is in generally good shape, since most of the lines are from electric dipole transitions whose intensities are well determined from Stark effect measurements; exceptions include some molecules with large vibration-rotation interactions (NO2) and internal motions (H2O2 above the lowest torsional state). The line parameters that are still the least well determined are pressure broadening coefficients, and their temperature coefficients, These are strongly dependent on the quantum states involved in the transitions, in a way that is much more complex than the simple projection by directional cosine matrix elements involved in determination of rotational line strengths from static dipole moments. The following molecules have now been measured or detected in the atmosphere using far infrared and millimeter-wave emission spectroscopy from balloon- and satellite-borne spectrometers: OH, HO2, H2O (including minor isotopomers and hot band lines), H2O2, O3P, O2 (including minor isotopomers), O3 (including minor isotopomers and hot band lines), HOCl, HCl, HF, HBr, CIO, CO, CO2, N2O, NO2, N2O5, HNO3, ClNO3, and HCN. Many of these species have spectral lines that are saturated in stratospheric spectra. In these cases, the measured line equivalent widths are proportional to (line strength x Lorentz width) (exp 1/2) so that the pressure broadening coefficients are as important as the line intensities in determining concentration profiles. Interpretation of field measurements for these species have required ongoing measurement programs of pressure broadening measurements. Other species (HO2, HGCl, H2O2, HBr, and NO2, as examples) have required further line position studies in order to fully analyze the field measurements.
Chance, Kelly V.↗
The effects of charged dust grains on IR molecular excitation
A number of issues involving grain charging in the interstellar medium were discussed. Such effects include: (1) stark broadening of molecular spectral features, (2) electrostatic grain rupturing, (3) enhancements in particle-grain collision cross sections, and (4) excitation of molecular rotations and/or vibrations.
Puetter, R.↗
Multiphonon Relaxation in Lacl sub 3 -Nd super 3 super plus
Multiphonon relaxation in neodymium doped lanthanum chloride, determining transition rates between stark levels with lifetime and quantum efficiency measurements
EMISSION SPECTRUM↗
Organic Cation Influence on Organic–Inorganic Thermal Equilibration within 2D Metal Halide Perovskites
Two-dimensional inorganic–organic lead halide perovskites exhibit tunable optoelectronic properties that are dictated by alternating layers of metal halide octahedra and organic cations. In such hybrid materials, vibrational coupling and thermalization between the low mass, insulating, organic cation spacers, and high mass inorganic octahedra remains poorly understood. Here, in this study, using femtosecond infrared-pump electronic-probe (IPEP) spectroscopy, we investigate the role of organic cation identity regarding the kinetics of vibrational energy exchange and sublattice mechanical coupling. Linear aliphatic cation-containing 2D perovskites with 4, 6, or 8 carbons (butylammonium = BA, hexylammonium = HA, and octylammonium = OA) were produced as thin films and mid-infrared pump pulses and then selectively excited organic cation stretch vibrations. Thermal energy introduction was evaluated via visible-wavelength optical probing that conveys inorganic octahedra response, owing to changes in electronic absorption. Multiple distinct spectral shifts appear upon excitation of the organic cations. Following an initial optical Stark shift caused by pump–probe temporal overlap, a redshift occurs within the first 10 ps that we attribute to compression of the octahedra by the expanded organic layers. Subsequently, a blueshift of the bandgap occurs commensurate with equilibration of both sublattices at an elevated temperature with a time constant of 21.8 to 31.6 ps depending on the spacer identity, with thermal energy transfer slowing by nearly 50% for the longest linker. By examining the effect that altered cation identity has on vibrational energy exchange, this work begins to offer routes to tune nonequilibrium response as well as provides insight into the fundamental impacts of organic spacers on thermal energy exchange in perovskite materials.
Peifer, Shoshanna E. [Northwestern Univ., Evanston↗
Ultrasonic/Sonic Impacting Penetrators
Ultrasonic/sonic impacting penetrators (USIPs) are recent additions to the series of apparatuses based on ultrasonic/sonic drill corers (USDCs). A USIP enables a rod probe to penetrate packed soil or another substance of similar consistency, without need to apply a large axial force that could result in buckling of the probe or in damage to some buried objects. USIPs were conceived for use in probing and analyzing soil to depths of tens of centimeters in the vicinity of buried barrels containing toxic waste, without causing rupture of the barrels. USIPs could also be used for other purposes, including, for example, searching for pipes, barrels, or other hard objects buried in soil; and detecting land mines. USDCs and other apparatuses based on USDCs have been described in numerous previous NASA Tech Briefs articles. The ones reported previously were designed, variously, for boring into, and/or acquiring samples of, rock or other hard, brittle materials of geological interest. To recapitulate: A USDC can be characterized as a lightweight, low-power, piezoelectrically driven jackhammer in which ultrasonic and sonic vibrations are generated and coupled to a tool bit. As shown in the figure, a basic USDC includes a piezoelectric stack, a backing and a horn connected to the stack, a free mass (free in the sense that it can slide axially a short distance between the horn and the shoulder of tool bit), and a tool bit, i.e., probe for USIP. The piezoelectric stack is driven at the resonance frequency of the stack/horn/backing assembly to create ultrasonic vibrations that are mechanically amplified by the horn. To prevent fracture during operation, the piezoelectric stack is held in compression by a bolt. The bouncing of the free mass between the horn and the tool bit at sonic frequencies generates hammering actions to the bit that are more effective for drilling than is the microhammering action of ultrasonic vibrations in ordinary ultrasonic drills. The hammering actions are so effective that the axial force needed to make the tool bit advance into the material of interest is much smaller than in ordinary twist drilling, ultrasonic drilling, or ordinary steady pushing.
Bao, Xiaoqi↗