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15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The Heat of Formation of HNO

The HNO molecule is of interest in both combustion and atmospheric chemistry. For example, Guadagnini et al. have recently presented ab initio potential energy surfaces for the three lowest lying electronic states of HNO and then used these in examining several chemical reactions that take place in the combustion of nitrogen containing fuels and in the oxidation of atmospheric nitrogen. We have previously studied the ground state potential energy surface (i.e., stationary points along the HNO rev. reaction HON path), vibrational spectrum (using an accurate quartic force field), zero-point energy, and bonding of HNO using coupled-cluster ab initio methods. HNO is also very interesting because of the unique nature of its bonding characteristics. That is, the potential energy surface is very flat along the H-N bonding coordinate thereby giving unusual harmonic and fundamental vibrational frequencies, and the H-N bond energy is rather weak in comparison to other H-N bond energies. In fact, using experimental heats of formation for HO, H, and NO, the H- bond energy is computed to be only 49.9 kcal/ mol (298 K). However, ab initio calculations of isodesmic reaction energies involving HNO, FNO, ClNO, and several other molecules have shown that there is an inconsistency in the experimental heats of formation of the XNO (X=H, F, and Cl) species. Hence the motivation for this study was to determine a very accurate(DELTA)H(sup o)(sub f) value for HNO using state of-the-art ab initio methods. Based on many recent studies it is evident that the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), in conjunction with large one-particle basis sets should be reliable to better than +0.8 kcal/mol for this quantity. The computational methodology is described in the next section followed by our results and discussion. Conclusions are presented in the final section.

Lee, Timothy J.↗
NASA NTRS1995

The Heat of Formation of HNO

The HNO molecule is of interest in both combustion and atmospheric chemistry. For example, Guadagnini et al. have recently presented ab initio potential energy surfaces for the three lowest lying electronic states of HNO and then used these in examining several chemical reactions that take place in the combustion of nitrogen containing fuels and in the oxidation of atmospheric nitrogen. We have previously studied the ground state potential energy surface (i.e., stationary points along the HNO reversible reaction HON path), vibrational spectrum (using an accurate quartic force field), zero-point energy, and bonding of HNO using coupled-cluster ab initio methods. HNO is also very interesting because of the unique nature of its bonding characteristics. That is, the potential energy surface is very flat along the H-N bonding coordinate thereby giving unusual harmonic and fundamental vibrational frequencies, and the H-N bond energy is rather weak in comparison to other H-N bond energies. In fact, using experimental heats of formation for HNO, H, and NO, the H- bond energy is computed to be only 49.9 kcal/ mol (298 K). However, ab initio calculations of isodesmic reaction energies involving HNO, FNO, ClNO, and several other molecules have shown that there is an inconsistency in the experimental heats of formation of the XNO (X double bond H, F, and Cl) species. Hence the motivation for this study was to determine a very accurate (Delta)H(sub f, sup o) value for HNO using state-of-the-art ab initio methods. Based on many recent studies it is evident that the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), in conjunction with large one-particle basis sets should be reliable to better than +/- 0.8 kcal/mol for this quantity. The computational methodology is described in the next section followed by our results and discussion. Conclusions are presented in the final section.

Lee, Timothy J.↗
NASA NTRS1994

An Accurate Quartic Force Field and Vibrational Frequencies for HNO and DNO

An accurate ab initio quartic force field for HNO has been determined using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, CCSD(T), in conjunction with the correlation consistent polarized valence triple zeta (cc-pVTZ) basis set. Improved harmonic frequencies were determined with the cc-pVQZ basis set. Fundamental vibrational frequencies were determined using a second-order perturbation theory analysis and also using variational calculations. The N-0 stretch and bending fundamentals are determined well from both vibrational analyses. The H-N stretch, however, is shown to have an unusually large anharmonic correction, and is not well determined using second-order perturbation theory. The H-N fundamental is well determined from the variational calculations, demonstrating the quality of the ab initio quartic force field. The zero-point energy of HNO that should be used in isodesmic reactions is also discussed.

Dateo, Christopher E.↗
NASA NTRS1984

Moisture dependence of positron annihilation spectra in nylon-6

Positron annihilation time spectra have been measured in nylon-6 samples as a function of their moisture content. The measured average long life component lifetime values are: 1722 + or - 47 ps (dry), 1676 + or - 40 ps (14.6 percent saturation value), 1719 + or - 26 ps (29.3 percent saturation value), 1720 + or - 35 ps (50 percent of saturation value), 1857 + or - 35 ps (78.1 percent saturation value), and 1936 + or - 57 ps (saturated). It appears that nylon-6 has a special affinity for water at low concentration levels where H2O molecules enter between the (C = O - H-N) chemical bonds between nylon molecular chains. As the water concentration increases beyond a critical level, nylon-6 specimens start trapping H2O molecules in other bond sites or potential wells. The trapped water increases the free volume in the test specimens and reduces Ps atom formation as well as its subsequent decay rate.

Singh, J. J.↗
NASA NTRS1994

Application of Coupled-Cluster Methods to the Prediction and Interpretation of the Spectra of Molecules of Interest in Atmospheric Chemistry

The quality of fundamental vibrational frequencies determined using the CCSD(T) method (singles and doubles coupled-cluster theory plus a perturbational estimate of the effects of connected triple excitations) is shown to be very good, usually predicting band centers to within +/-8/cm. This approach is applied to several molecules of interest in atmospheric chemistry, including HNO, NO2(+), H2CO, and HOCl. The HNO molecule displays a large and unusual anharmonicity in the H-N stretch. For the calculation of ultraviolet (UV) spectra, the linear response CCSD (LRCCSD) approach (which is equivalent to EOM-CCSD) has been shown to yield vertical excitation energies that are accurate to approximately 0.1 eV for singly excited electronic states. This method together with more approximate methods is used to examine the UV spectra of several molecules important in stratospheric chemistry, including HOCl, Cl2O, ClOOCl, ClOOH, and HOOH.

Lee, Timothy J.↗
NASA NTRS1994

Aqueous Phase Non Enzymatic Chemistry of Cyanide, Formaldehyde and RNH2

It is postulated that amino acids were produced on the early earth from dilute aqueous solution of cyanide, carbonyls and ammonia (the Strecker synthesis RNH2 + R"R""C=O + KCN yields H-N(R)-C(R")(R"")-CO2H. We have studied the products obtained from dilute aqueous solutions of cyanide, formaldehyde (R"=R""=H), ammonia (R=H) and amino acids. Solutions in the pH range from 8 to 10. at room temperature and at reactant concentrations from 0.001 M to 0.3 M have been studied. With R= H product yields were low (less than 3%). Only with R"=R""=H and R represented by the following: CH2CO2H (glycine); CH(CH3)CO2H (alanine); CH(CH2CH3)CO2H (a-amino n=butyric acids); C(CH3)2(CO2H) (a-aminoisobutyric acid); CH(CH(CH3)2)CO2H (valine); and CH(CH2CO2H)CO2H (aspartic acid), were product yields high (greater than 10%). The yields of glycine were larger with R not equal to H. The prebiotic implications of these findings will be discussed.

Lerner, Narcinda R.↗
NASA NTRS1995

Ab Initio Studies of Fluorine and Chlorine Oxide and Nitrogen Oxide Species of Interest in Stratospheric Chemistry

The quality of fundamental vibrational frequencies determined using the CCSD(T) method (singles and doubles coupled-cluster theory plus a perturbational estimate of the effects of connected triple excitations) is shown to be very good, usually predicting band centers to within plus or minus 8 per centimeter. This approach is applied to several molecules of interest in atmospheric chemistry, such as HNO, cis-FONO, cis-ClONO, and ClOOH. The HNO molecule displays a large and unusual anharmonicity in the H-N stretch. For the calculation of ultraviolet (UV) spectra, the linear response CCSD (LRCCSD) approach (which is equivalent to EOM-CCSD) has been shown to yield vertical excitation energies that are accurate to approximately equal to 0.1 eV for singly excited electronic states. This method together with more approximate methods is used to examine the UV spectra of several molecules important in stratospheric chemistry, including HOCl, Cl2O, ClONO2, HONO2, ClOOCl, ClOOH, and HOOH.

Lee, Timothy J.↗
NASA NTRS1995

Ab Initio Potential Energy Surfaces and the Calculation of Accurate Vibrational Frequencies

Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within plus or minus 8 cm(exp -1) on average, and molecular bond distances are accurate to within plus or minus 0.001-0.003 Angstroms, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as vibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy will be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.

Lee, Timothy J.↗
NASA NTRS1996

Ab Initio Calculation of Accurate Vibrational Frequencies for Molecules of Interest in Atmospheric Chemistry

Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within +/- 8 cm(sup -1) on average, and molecular bond distances are accurate to within +/- 0.001-0.003 A, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as rovibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy win be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.

Lee, Timothy J.↗
DOE OSTI2020

Materials Data on HN by Materials Project

(N2)3(NH4)2 crystallizes in the orthorhombic Pmna space group. The structure is zero-dimensional and consists of four ammonium molecules and four triazane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H3N by Materials Project

NH3 is Ammonia structured and crystallizes in the cubic P2_13 space group. The structure is zero-dimensional and consists of four ammonia molecules. N3- is bonded in a trigonal non-coplanar geometry to three equivalent H1+ atoms. All N–H bond lengths are 1.03 Å. H1+ is bonded in a single-bond geometry to one N3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H3N by Materials Project

NH3 is Ammonia-like structured and crystallizes in the orthorhombic P2_12_12_1 space group. The structure is zero-dimensional and consists of four ammonia molecules. N3- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. All N–H bond lengths are 1.03 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HN by Materials Project

N4H3NH2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four ammonia molecules and four N4H3 clusters. In each N4H3 cluster, there are four inequivalent N1- sites. In the first N1- site, N1- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. There are a spread of N–H bond distances ranging from 1.05–1.08 Å. In the second N1- site, N1- is bonded in a linear geometry to two N1- atoms. There is one shorter (1.18 Å) and one longer (1.19 Å) N–N bond length. In the third N1- site, N1- is bonded in a distorted bent 120 degrees geometry to one N1- and one H1+ atom. The N–H bond length is 1.71 Å. In the fourth N1- site, N1- is bonded in a single-bond geometry to one N1- atom. There are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to two N1- atoms. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N1- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H3N by Materials Project

NH3 is Ammonia-like structured and crystallizes in the cubic P2_13 space group. The structure is zero-dimensional and consists of four ammonia molecules. N3- is bonded in a trigonal non-coplanar geometry to three equivalent H1+ atoms. All N–H bond lengths are 1.02 Å. H1+ is bonded in a single-bond geometry to one N3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H4N by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗