Hoang Dothe

Vibrational structure of the solvated glycine zwitterion

Abstract The vibrational frequencies of glycine in aqueous solution are calculated. The effects of the water—glycine interactions on the forces and force constants of glycine, calculated using an ab initio SCF method, are treated by means of a molecular dynamics simulation of a system consisting of a glycine molecule surrounded by 253 water molecules. These interactions cannot be ignored because the isolated glycine zwitterion is unstable and is stabilized by the solvation. The fundamental frequencies of the glycine zwitterion and three of its deuterated isotopomers were calculated from the molecular dynamics forces and force constants. The resulting frequencies, after scaling with a single factor for the four isotopomers, are in good agreement with the experimental results.

Comment Comparison of ab initio and scaled quantum mechanical methods for the calculation of vibrational structure: A reply to bose and polavarapu

Abstract Recent criticisms by Bose and Polavarapu of the scaled quantum mechanical (SQM) force field method for the calculation of vibrational structure are discussed. The SQM method can give quantitatively accurate frequencies, force constant matrix elements, and potential energy distributions of molecules, while the corresponding ab initio calculation using the same basis set can fail to give even qualitative agreement with experiment. The SQM method can be employed for molecules whose vibrational assignment is uncertain by transferrring SQM scale factors from related molecules. For molecules without symmetry whose vibrational assignment is certain, the SQM method is equivalent to an ab initio calculation in which all calculated frequencies are scaled using a single multiplicative factor.

Scaled quantum mechanical calculations of the vibrational structure of thiirane, thiirene, and their deuterated isotopomers

Abstract The scaled quantum mechanical (SQM) method for calculating the vibrational structure of molecules is applied to thiirane, thiirene, and their deuterated isotopomers. The purpose of these calculations is to test the method against the experimental spectra and recent ab initio calculations of these molecules. It is found that the SQM method implemented with the 6-31 G* basis set at the experimental geometry for the thiiranes and with the 6-31 G* set at the 6-31 G* corrected theoretical geometry for the thiirenes gives excellent agreement with experiment and with the largest of the ab initio calculations.

NLTERAD (Non-local thermodynamic equilibrium radiance) Model

This paper presents an UltraViolet-Visible (UV-Vis) spectral radiance simulation capability for Non-Local Thermodynamic Equilibrium (non-LTE) conditions, consisting of a full line-by-line (LBL) radiative transfer (RT) algorithm and a UV-Vis signatures library. Results are presented for two example scenarios where strong UV-Vis emissions arise, an atmospheric high altitude auroral event and a High Explosive (HE) detonation.

Characterizing temperature and water vapor of the environment using the standardized atmosphere generator (SAG) empirical model

Optimal interpretation of remote sensing imagery requires characterizing the atmospheric composition between a sensor and the area it is observing. Timely estimates of atmospheric temperature, water vapor, and other constituents from the ground to the edge of the space environment are not always readily available. In those cases, we must supplement our knowledge of the atmosphere’s composition to fill in any gaps in knowledge and empirical models of the atmosphere are useful tools for this purpose. The Standardized Atmosphere Generator (SAG) was constructed is one such empirical. It has been designed to allow all the major known, systematic variability in the atmosphere and may be used to generate atmospheric profile from the ground to 300 km consistent with user-specified temporal, geophysical, and geographical information Output provides reasonable estimates for temperature, pressure, and densities of atmospheric constituents and can be directly incorporated into radiative transfer forward models or retrieval algorithms. SAG draws upon a number of existing empirical atmospheric models and ensures consistency of output between them. It can be used either as a stand-alone interactive program or scripted for batch execution and assist in determining atmospheric attenuation, refraction, scattering, chemical kinetic temperature profiles, and a host of other naturally occurring processes. Here, we will discuss the capabilities and performance of the SAG model for a variety of applications including its interactive and batch processing use. We will also demonstrate the physical realism of SAG through a small number of relevant use cases.