Journal of Quantitative Spectroscopy & Radiative Transfer最新文献

A continuous-wave cavity ring-down spectrometer was employed to record the spectrum of the acetylene molecule spanning the 12350 - 12790 cm⁻¹ region. A total of 747 lines from the principal isotopologue and 68 lines from ¹²C¹³CH${}_2$ were identified, with nearly all line intensities retrieved from the spectra. These lines belong to eighteen vibrational bands of ¹²C${}_2$H${}_2$ and two vibrational bands of ¹²C¹³CH${}_2$, among which five vibrational bands are reported here for the first time. Spectroscopic constants were deduced for all the identified bands, and the vibrational dipole moment squared along with Herman–Wallis coefficients were determined for the majority of these bands. Additionally, several resonance interactions were thoroughly explored.

The N${}_2-$N${}_2$  and N${}_2-$Ar continuum absorption spectra are calculated using the classical trajectory-based simulation (CTS). The spectra obtained are validated by new measurements in the subTHz spectral range along with the previously reported data in the far infrared. A novelty of our approach consists in the use of the CTS method to simulate both the fundamental nitrogen absorption band and the rototranslational band in N${}_2-$Ar , i.e., we succeeded to step beyond the conventionally used approximation of the only rigid monomers. This extension of the theory made it possible, in particular, to demonstrate the validity of the rigid monomer assumption for the CTS simulation of the rototranslational N${}_2-$Ar band. The broadband spectra within 77–354 GHz were measured using the resonator spectrometer at temperatures of 278–333 K and pressures of 900–1600 Torr. A minor underestimation of the calculated absorption by 3.7% and 5% is shown for the N${}_2-$N${}_2$  and N${}_2-$Ar system, respectively. On the basis of the obtained data, a new analytical model is developed for the N${}_2-$N${}_2$  absorption in the subTHz range, which can be used in radiation propagation codes for the Earth, Titan, or other nitrogen-rich atmospheres. The advantage of the model proposed here over those previously published is discussed.

In this work, we calculated Stark broadening widths of several doubly-ionized chlorine Cl III spectral lines using the modified semi-empirical approach. The theoretical values of Stark widths are calculated using term energies and oscillator strengths of Cl III from the AUTOSTRUCTURE atomic structure code. We compared the calculated Stark widths with available data from the literature. If we need to interpolate these Stark widths at different temperatures for the studied transitions of Cl III, we use a simple and accurate fitting formula based on a least-squares fitting method.

Accurate estimation of solar power generation is crucial for the effective planning and operation of solar energy sector. Solar potential can be estimated at a location from long-term historical irradiance data processed from atmospheric reanalysis datasets. The current study employs a clear-sky radiative transfer model (6S) to simulate the net surface irradiance at four distinct locations in India, comparing our model's output with mean monthly ground-based measurements of surface irradiance. Our findings reveal that the 6S model marginally underestimates solar irradiance, with potential deviations varying depending on the accuracy of input data. This research evaluates the influence of particulate matter concentration and relative humidity on the scattering and absorption of solar radiation. We also state the variability in surface irradiance across the country with the rainfall trends that enhance assessment accuracy. The study reports an annual deviation of 10–15 % in surface irradiance across the country, where rural settlements show lower deviations in simulations. The radiative transfer calculations mentioned in the study are simplistic yet beneficial for a priori evaluation of solar potential. Transmittance estimated from clear-sky models is further implemented in all-sky (with clouds), and thus, model accuracy is an important parameter. Additionally, we explore the trends in aerosol concentrations and the impact of local climatological factors on surface irradiance, providing insights critical for optimizing solar energy utilization.

We investigated the molecular structure and spectroscopic properties of the charged system (FH⁺) in interaction with a helium atom using an ab initio quantum chemistry approach in Jacobi coordinates. Our study focused on the ground state X²Π of (FH⁺) with various theoretical methods including UCCSD, UCCSD(T) and UCCSD(T)-F12, alongside basis sets like aug-cc-pVnZ (n = T, Q, 5, and 6) and cc-pVQZ-F12. We evaluated how these methods and basis sets affect the minimum energies We assessed the impact of the methods, basis sets, and extrapolation approaches on the minimum energies. Potential energy surfaces (PES) were generated using the correlated UCCSD(T)-F12 method with cc-pVQZ-F12 for hydrogen and fluorine, and cc-pVQZ-F12/optri for helium. These surfaces, considering spin-orbit coupling, are degenerate for linear geometries (θ=0° and θ=180°) of the (FH+)-He complex and correlate with the doubly degenerate X²Π state of (FH⁺). Our results reveal a strong anisotropic character at short and intermediate distances and a quasi-isotropic character upon dissociation into FH⁺ and He. We compared the spectroscopic parameters of the (FH⁺)-He complex with existing theoretical data, finding that the linear arrangement exhibits the highest stability, consistent with previous results for similar complexes. This conclusion is supported by the Milliken atomic charge distribution and a three-dimensional map of the Molecular Electrostatic Potential. Additionally, we used the LEVEL program, to calculate the bound rovibronic levels of the (FH⁺)-He complex for angular momentum values Ω=1/2 and Ω=3/2. Utilizing our ab initio results and a general interpolation approach based on the Reproducing Kernel Hilbert Space method, we generated contour maps illustrating the analytical potential for the (FH⁺)-He system. These findings will be employed to study the stabilities, geometries, energetics, and structures of the FH⁺ charged system within helium clusters.

The discrete system Green’s function (DSGF) method is a fluctuational electrodynamics-based numerical framework for predicting near-field radiative heat transfer (NFRHT) between three-dimensional thermal sources of arbitrary number, shape, size, and material. In the DSGF method, thermal sources are discretized into cubic subvolumes along a cubic lattice, and the system Green’s functions between all subvolumes are obtained by solving a system of linear equations. From the system Green’s functions, quantities of interest in heat transfer such as the power dissipated and the thermal conductance are calculated. The objective of this paper is to provide a user guide of the DSGF solver publicly available on GitHub. The basics of the DSGF method are first reviewed, followed by a detailed description of the DSGF solver implemented in MATLAB and C. The C implementation is parallelized and includes an iterative procedure which is not available in the MATLAB version. Example problems of NFRHT between two dipoles, two spheres, two cubes, and two membranes that can be used for verification are provided.

This study utilized the high-spectral resolution radiative transfer model (MODerate resolution atmospheric TRANsmission, MODTRAN6.0.2.5) to compute global clear-sky shortwave (SW) radiative flux and compared it with NASA’s Clouds and the Earth’s Radiant Energy System (CERES) Synoptic Radiative Fluxes and Clouds (SYN1deg) product. The comparison revealed that the global distributions of clear-sky downwelling SW fluxes at the surface from the M6.0 calculations and SYN1 results are similar, with annual means of 246.51 Wm^-2 and 242.42 Wm^-2, respectively. Analysis further showed that most of the M6.0 calculations are slightly higher from low to mid-latitudes, particularly in the Northern Hemisphere (NH), but lower in higher latitudes compared to SYN1 results. However, these differences mostly fall within the CERES estimated uncertainty (6 Wm^-2) of monthly mean clear-sky downwelling SW flux at the surface. The sensitivity of clear-sky SW/${\mu }_0$ fluxes to changes in Precipitable Water Vapor (PWV), represented by the clear-sky water vapor radiative kernel, is about -0.7 Wm^-2/(kgm^-2) over oceans for both M6.0 and CERES SYN1 products, except for SYN1 results over the Southern Hemisphere (SH) ocean. Additionally, the zonal means of land coverage and SW/VIS/NIR albedos from M6.0 calculations indicate that VIS albedos are highest in polar regions ($>$60°), followed by SW and NIR albedos, while NIR albedos become highest from low to mid-latitudes ($<$60°). Generally, SW/VIS/NIR albedos and their differences increase monotonically with increased land coverage from 60°S to 60°N. The consistent clear-sky water vapor radiative kernels derived from both products exceeded our expectations, suggesting their potential use to trace physical signatures in climate model calculations. It is recommended that these model-derived radiative kernels should be validated by the long-term global and regional surface observations in order to enhance confidence to implement these radiative kernels in climate models.

In this study the clear-sky total, direct, and diffuse shortwave (SW) fluxes at the surface, have been calculated by three radiation transfer models (RTMs) – MODTRAN6.0 (M6.0), Canadian Centre for Climate Modelling and Analysis (CCCma), and Langley-modified Fu-Liou (NASA CERES). These calculations have been evaluated by surface measurements collected from seven sites that represent different climatological regimes with various surface scene types including ocean, grassland/continental, desert, and snow/sea ice. For pristine atmospheric conditions, SW fluxes predicted by CCCma and M6.0 shows little variation, which lays a baseline for further analysis. Note that computing time required by CCCma is ∼1000 times smaller than M6.0. Based on all samples collected from seven sites, mean differences of total, direct, and diffuse fluxes between surface measurements and CCCma / M6.0 / Fu-Liou are [5.3 / 2.4 / 0.9], [-2.2 / -5.1 / -13.7], and [7.5 / 7.5 / 14.6] W m^-2, respectively. Histograms of differences between the three RTM calculations and surface measurements show that CCCma computed direct and diffuse fluxes have the smallest biases with standard deviations similar to those for M6.0, while Fu-Liou values have the largest biases and standard deviations. While Fu-Liou outperforms for total flux, especially for desert conditions, it is hampered by large biases for direct and diffuse across all scene types. The three RTMs are consistent with showing the least error for total flux and the largest in diffuse based on bias, correlation, and root mean square error.

Collisional broadening and pressure shift parameters for the potassium resonance doublet, near 770 nm, are reported for collisions with molecular oxygen and carbon dioxide. Experiments were conducted in a reflected shock tube from 1200–2200 K and used potassium chloride (KCl) salt as the atomic potassium source. The measured absorption lineshapes were fit with Voigt profiles to infer the collisional broadening and pressure shifts. Power-law correlations were then developed to describe the pressure-normalized results as functions of temperature. Generally, the collisional broadening coefficients in oxygen agree well with theoretical predictions and are similar to those in nitrogen. Conversely, the pressure shift coefficients in oxygen differ from those in nitrogen by up to 15%. Broadening coefficients in carbon dioxide disagree with theoretical predictions by 20% or more over the range of temperatures explored in this work. These results expand the existing database of potassium lineshape coefficients, and they are expected to be useful for further development of potassium sensing diagnostics in terrestrial, Martian, and Venusian atmospheric flight studies, and in combustion systems. Other anticipated applications include interpretation of astrophysical spectroscopic observations.

We study the resonant saturation of selective reflection at the interface between a transparent dielectric and high-density rubidium vapor on the D${}_2$-line. Our estimates suggest that, within the selected atomic density range, the dipole–dipole self-broadening of the line can vary from 13.2 to 39.6 GHz. Two tunable lasers are used as sources of pump and probe beams with orthogonal linear polarizations. The selective reflection spectra of the probe laser beam are studied at different atomic densities and pump beam intensities ranging from 0 to 8.8 kW cm⁻². At high pump intensities, narrow structures are observed around the pump beam frequency, which are associated with power broadening effects. Increasing the pump intensity reduces the spectral width and the magnitude of the selective reflection resonances. The intensity dependence of the width and the magnitude is measured. By adjusting the pump intensity, it is possible to control the spectral width and reflectivity.