Spectra Of Ammonia Research Articles

The spectroscopy of high Rydberg states of ammonia

This paper extends our knowledge of the higher excited states of the ammonia molecule by presenting detailed measurements of the 2+1 resonance enhanced multiphoton ionization (REMPI) spectrum of both NH3 and ND3 obtained following excitation in the wavelength range 298–242 nm, i.e., at energies up to the first ionization energy. Complementary analyses of the wavelength resolved REMPI spectrum and the accompanying REMPI-photoelectron spectra leads to the identification of ten new Rydberg origins of NH3 (four for ND3) with principal quantum numbers n⩽8 and, in most cases, of the accompanying out-of-plane bending vibrational progression. Symmetry assignments for the various newly identified excited states are offered, based on band contour simulation and/or quantum defect considerations. Dominant amongst these are the Ẽ″ 1A2″ (5sa1′←1a2″) state: ν0=74 118(2) cm−1 [NH3], ν0=74 258(2) cm−1 [ND3], the F̃″ 1E″ (5pe′←1a2″) state: ν0=76 220(50) cm−1 [NH3], ν0=76 240(50) cm−1 [ND3], the F̃′ 1A1′ (5pa2″←1a2″) state: ν0=76 674(1) cm−1 [NH3], ν0=76 770(5) cm−1 [ND3], and the G̃′ 1A1′ (6pa2″←1a2″) state: ν0=78 494(1) cm−1 [NH3]. The present work serves to reinforce the previously noted dominance of np←1a2″ Rydberg excitations in the 2+1 REMPI spectrum of ammonia. In addition, the adiabatic ionization energy of ND3 is estimated to be 82 280±40 cm−1 based on the assumption that analogous Rydberg states of NH3 and ND3 will have very similar quantum defects.

A method of calculating adsorption enthalpy distribution using ammonia temperature-programmed desorption spectrum under adsorption equilibrium conditions

A method, called the ac-TPD method, was presented for calculating the density distribution function of the adsorption enthalpy of ammonia by utilizing the temperature-programmed desorption (TPD) spectrum of ammonia from solid catalysts measured under complete adsorption equilibrium conditions. TPD spectra were measured using a gas stream containing ammonia, at a relatively large concentration compared to the amount of ammonia desorbed from the catalyst. Under these conditions, the concentrations of ammonia both inside the catalyst particles and in the gas phase are kept almost constant during the experiment. This situation meant that the amount of ammonia remaining on the catalyst was at an equilibrium state and dependent on the temperature and concentration of ammonia. Therefore, it could be assumed that the adsorption equilibrium of ammonia on acid sites can be expressed by a Langmuir-Hinshelwood type equation, which has an adsorption enthalpy and a pre-exponential adsorption equilibrium constant corresponding to the strength of an acid site. The overall TPD spectrum is represented by the sum of the spectra from acid sites with different acid strengths. Under these assumptions, the desorption temperature was related to the adsorption enthalpy of ammonia, and a relationship was derived between the overall TPD spectrum and the density distribution function of the adsorption enthalpy. The distribution function obtained by this method can be used for evaluating acidic properties of solid catalysts. The heat flux required for the desorption of ammonia from acid sites during the TPD experiment was calculated using the obtained distribution. The value was found to agree well with that directly measured by a differential scanning calorimetric apparatus. The density distribution of the adsorption enthalpy ( Q) was compared to the distribution of activation energy for desorption of ammonia ( E) by a method, called dc-TPD, which was reported previously by us. This comparison gave the relationship between Q and E, and it was found that the Q value was smaller than the E value by about 15 kJ mol −1.

Selective nuclear hydrogenation of naphthalene, anthracene and coal-derived oil over Ru supported on mixed oxide

The main objective of this paper is to investigate the possible ways to produce high-quality products for transportation fuels from heavy distillates. For this purpose, 0.1, 0.2, 0.5, and 1.0 wt% Ru, supported on three kinds of metallic oxide supports, Ru/Mn 2O 3 ZnO, Ru/Mn 2O 3 NiO and Ru/Mn 2O 3 La 2O 3, were used as catalysts for selective nuclear hydrogenation of naphthalene, anthracene, and Canadian Battle River-coal-derived oil. The catalysts exhibited activity in the following order: Ru/Mn 2O 3 NiO>Ru/Mn 2O 3 ZnO>Ru/Mn 2O 3 La 2O 3. The Ru/Mn 2O 3 NiO catalyst showed the lowest exothermic temperature, corresponding to a decrease of differential pressure of hydrogen observed in the high-pressure DTA, and gave the largest H/Ru values among the catalysts determined by hydrogen chemisorption. The Ru/Mn 2O 3(0.19) NiO(0.81) among them showed the best performance for the reaction; it yielded 33 mol% of decalins from naphthalene and 49 mol% of perhydroanthracene from anthracene. The catalyst also converted 59 mol% of aromatic hydrogen to hydrogen at β- and γ-positions of aromatic hydrocarbons in the coal liquid. The temperature-programmed desorption (TPD) spectra of hydrogen and ammonia on the catalysts were measured to find the influence of acidity of supports for the catalytic activity. It was concluded that Ru on nonacidic support, which is Mn 2O 3 NiO, showed the best performance, and a 0.1 wt% Ru loading on the Mn 2O 3 NiO was sufficiently effective for the selective nuclear hydrogenation.

A method for calculating the activation energy distribution for desorption of ammonia using a TPD spectrum obtained under desorption control conditions

A method, called the dc-TPD method, was presented for calculating the density distribution function of the activation energy for ammonia desorption by utilizing the temperature-programmed desorption (TPD) spectrum of ammonia from solid catalysts measured under desorption control conditions. TPD spectra were measured in a helium stream under low pressure (about 0.13 kPa) to realize desorption control conditions by removing ammonia desorbed from a catalyst quickly. The measured TPD spectra showed only one peak corresponding to stronger acid sites, and were found to be dependent not on the time factor (ratio of the catalyst weight to the gas flow rate), but only on the heating rate. The TPD spectrum thus obtained was assumed to be the sum of the spectra from a series of acid sites with different acid strengths distributed on the catalyst. The desorption of ammonia from the acid sites was approximated as an irreversible first-order reaction rate equation with the activation energy and frequency factor whose values correspond to the acid strength of the acid sites. Using these assumptions, the relation between the TPD spectrum and the activation energy distribution for desorption was derived. The distribution functions obtained can be used for characterizing the acidic properties of solid catalysts. The shape of the distribution function was found to have little dependence on the heating rate in the TPD experiment. The acidic properties of silica-alumina, H-mordenite, and HY-type and MFI-type zeolites were well characterized by the distribution function of the activation energy for ammonia desorption.

CO 2-laser photoacoustic spectroscopy of deuterated ammonia

Photoacoustic (PA) coincidence absorption spectra of ammonia and its deuterated forms with carbon-dioxide laser emission were obtained. In addition, a simple isotope synthesis procedure was developed for that purpose. The strongest coincidence for the NH 3 molecule was found with laser line 9R(30) at 1084.628 cm −1. Laser PA spectra of samples with different deuterium content indicate that coincidences with laser lines 10R(14) and 10R(30) at 971.93 and 982.10 cm −1, respectively, correspond to NH 2D, while one with 10R(20) at 975.93 cm −1 is attributed to NHD 2. The data obtained are discussed in relation to their uses in isotope chemistry and analysis. They are in agreement with results published by other authors.

Far-infrared absorption spectra of water, ammonia, and chloroform calculated from instantaneous normal mode theory

Instantaneous normal mode (INM) theory was used to calculate absolute far-infrared absorption spectra of water, ammonia, and chloroform. Three procedures for weighting the INM density of states to yield absorption intensities were tested against spectra based on dipole time correlation functions generated from molecular dynamics (MD) simulations. Weighting method I, which utilizes only the rotational character of a mode in determining its contribution to absorption, performed slightly better than method II, a more exact treatment which incorporates the extent to which a mode is IR-active. Method III, which includes the contributions of induced dipoles, was successful in describing the influence of induced dipoles on the far-infrared spectra of the model liquids. The contribution to absorption of unstable modes with imaginary frequencies was found to be significant at low frequencies, and was treated by a simple approximation. Agreement between INM theory and the MD analysis was quite good for chloroform and ammonia, but less so for water. Agreement with experimental data in the range of 4–100 cm−1 was generally poor, but no worse than that for the MD calculations, primarily reflecting the simple intermolecular potentials used rather than the computational method itself.

The structure of the boron trifluoride-ammonia complex: a Fourier transform matrix isolation infrared spectroscopic and ab initio molecular orbital study

The structures, interaction energies and Mulliken atomic charges of the 1:1 electron donor-acceptor complexes formed between boron trifluoride and ammonia have been determined by means of ab initio molecular orbital calculations. The calculations have been extended to include a prediction of the infrared spectra of the complexes, leading to the identification of the staggered conformer as the minimum energy structure and the eclipsed species as a transition state. The computed wavenumber shifts of the complex bands, relative to their positions in the monomers, and the complex/monomer infrared band intensity ratios have been determined and rationalized in the light of the nature and strength of the interaction. The infrared spectra of boron trifluoride and ammonia co-deposited in nitrogen and argon matrices have been recorded at cryogenic temperatures. The spectra have been interpreted in terms of the Lewis acid-base complex predicted theoretically to be the preferred structure, and band assignments proposed for most of the complex bands. The spectroscopic properties derived experimentally and theoretically have been compared with one another.

Ro-inversional Spectrum of Ammonia

The ground state J = 2 ←1 , K = 0 and K = 1 ro-inversional spectrum of 14NH3 and 15NH3 at 1.2 THz has been measured with an accuracy of 20 kHz using the Cologne terahertz spectrometer. The measured frequencies for the K = 0 components are: 14NH3 (J, K) = a(2, 0) - s( 1,0): 1 214 852.942(20) MHz, 15NH3 (J, K) = a(2, 0 ) - s( 1,0) : 1 210 889.556(20) MHz. In addition we have determined from saturation dip measurements of the J = 1 - 0 transition the spin-rotation constant CN = 6.7(3) kHz and the unsplit line center frequency: 14NH3 (J, K) = s( 1, 0) - a(0, 0): 572 498.163( 10) MHz. The new results are in excellent agreement with existing high resolution Fourier transform data. The terahertz line frequencies are of considerably higher accuracy than the FT-data. by about two orders of magnitude. They will serve as future calibration lines. The ro-inversional transitions are of astrophysical interest

Vibrational infrared spectrum of NH3 adsorbed on MgO(100). II. Interatomic potential calculations

Abstract Interatomic potential calculations are used to determine the main characteristics of the infrared spectrum of ammonia adsorbed on MgO. The frequencies and intensities of the vibrational bands for the single admolecule and for the addimer (NH 3 ) 2 compare fairly well with the results issued from ab initio calculations of paper I. This indicates that the semiclassical approach is convenient for describing adsorption characteristics, at least within the physisorption scheme for which electrostatic and dispersion-repulsion potential interactions are dominant. The bar infrared spectrum is then drawn and compared to the experimental spectra recorded at 300 K and at low and medium coverages. The frequency regions associated with the bands around 1100 and 3300 cm −1 and assigned to the ν 2 and ν 1 symmetric modes are interpreted in terms of vibration-libration Q peaks. The bands at about 1600 and 3400 cm −1 , characteristics of the initially twofold degenerate ν 4 and ν 3 vibrations, exhibit rotational structures due to the quasi-free spinning motion of the protons in the adsorbed NH 3 molecule. From this quantitative analysis, other adsorption sites which cannot be accounted for by a physisorption model, must be invoked to interpret the whole shape of the infrared profile.

Five-dimensional local mode-Fermi resonance model for overtone spectra of ammonia

A five-dimensional local mode-Fermi resonance model for overtone spectra of the ammonia molecule has been constructed. The model Hamiltonian is expressed in terms of curvilinear internal valence coordinates and it includes the three stretching vibrations and the doubly degenerate bending vibration. The symmetric bending vibration associated with the inversion motion has been excluded. Thus the model is useful for energy levels with the totally symmetric bending vibration on its ground state. Vibrational energy levels have been calculated using van Vleck perturbation theory. Nonlinear least-squares method has been used to optimize potential energy parameters. Observed vibrational band origins for 14NH3, 14ND3, and 14NT3 have been employed as data. A fit with the standard deviation of 5.5 cm−1 has been obtained using one set of isotope invariant potential energy parameters. The optimised potential energy surface compare well with results of ab initio electronic structure calculations and with results of customary anharmonic force field calculations.

Process for making alkylated polycyclic aromatics

The main objective of this paper is to investigate the possible ways to produce high-quality products for transportation fuels from heavy distillates. For this purpose, 0.1, 0.2, 0.5, and 1.0 wt% Ru, supported on three kinds of metallic oxide supports, Ru/Mn2O3ZnO, Ru/Mn2O3NiO and Ru/Mn2O3La2O3, were used as catalysts for selective nuclear hydrogenation of naphthalene, anthracene, and Canadian Battle River-coal-derived oil. The catalysts exhibited activity in the following order: Ru/Mn2O3NiO>Ru/Mn2O3ZnO>Ru/Mn2O3La2O3. The Ru/Mn2O3NiO catalyst showed the lowest exothermic temperature, corresponding to a decrease of differential pressure of hydrogen observed in the high-pressure DTA, and gave the largest H/Ru values among the catalysts determined by hydrogen chemisorption. The Ru/Mn2O3(0.19)NiO(0.81) among them showed the best performance for the reaction; it yielded 33 mol% of decalins from naphthalene and 49 mol% of perhydroanthracene from anthracene. The catalyst also converted 59 mol% of aromatic hydrogen to hydrogen at β- and γ-positions of aromatic hydrocarbons in the coal liquid. The temperature-programmed desorption (TPD) spectra of hydrogen and ammonia on the catalysts were measured to find the influence of acidity of supports for the catalytic activity. It was concluded that Ru on nonacidic support, which is Mn2O3NiO, showed the best performance, and a 0.1 wt% Ru loading on the Mn2O3NiO was sufficiently effective for the selective nuclear hydrogenation.

The distribution of activation energy for hydrogen desorption over silica-supported nickel catalysts determined from temperature-programmed desorption spectra

A method has been developed that can calculate the distribution of activation energy for desorption of hydrogen from temperature-programmed desorption (TPD) spectra for characterizing the heterogeneity of the surfaces of supported metal catalysts. This method is based on the idea of Hashimoto et al. [Stud. Surf. Sci. Catal. 28 (1986) 503] who determined the distribution of acid strength of solid acid catalysts from the TPD spectra of ammonia. The surface of a catalyst is regarded as a collection of groups of desorption sites with identical activation energy in each group. These groups are experimentally sampled from a series of TPD spectra and a set of desorption kinetic parameters are determined for each group. An overall TPD spectrum is given by the summation of the contribution from each group characterized by a particular activation energy. The fitting of a calculated spectrum to an experimental one determines the activation energy distribution. This method has been applied to study the surfaces of silica-supported nickel catalysts in the present work. The surface state of the catalysts is influenced by various preparation variables, and their influence is expressed in terms of the distribution of activation energy for hydrogen desorption.

Investigation of absorption spectra of acetone and ammonia in the generation range of a waveguide co laser, by means of an optothermal detection method

Investigation of absorption spectra of acetone and ammonia in the generation range of a waveguide co laser, by means of an optothermal detection method

Preparation of a dense ZSM-5 zeolite film on the outer surface of an alumina ceramic filter

Thin films of ZSM-5 zeolite were prepared on the outer surface of an alumina ceramic filter by hydrothermal synthesis at 473 K. Their structure and atomic composition were shown to be the same as those of the corresponding original zeolite using several spectrometric methods: X-ray diffraction, 29Si magic angle spinning nuclear magnetic resonance and electron probe microanalysis. The acidic properties of the membrane were evaluated using the conventional temperature-programmed desorption spectrum of ammonia. The morphology and thickness of the zeolite film were dependent on the silica source. Water glass is typically used as the silica source in the preparation of powdery ZSM-5 zeolite. A dense zeolite film could be prepared using Na 2SiO 3 as the silica source, but could not be obtained using water glass as the silica source.

Luminescence and IR Characterization of Acid Sites on Alumina

Luminescence and infrared (IR) spectroscopies of pyridine and ammonia adsorption have been used to measure acidities of γ-alumina. Neither luminescence nor IR spectra of pyridine adsorption show any Brønsted acidity on γ-alumina pretreated at 400°C. However, luminescence emission data reveal four weak OH bands even when pretreatment is done at 600°C. Pyridine and subsequent water adsorption yield six luminescence emission bands. A red shift of the pyridine emission band is found when pretreatment or desorption temperature is increased. IR spectra of ammonia on alumina pretreated at 400°C show three deformation bands at 1452, 1465, and 1485 cm−1. The first band is also observed together with a band at 1554 cm−1 even for pretreatment at 950°C, and it corresponds to NH+4 formed from dissociative adsorption of ammonia, while the other two bands are assigned to ammonia adsorbed on Brønsted acid sites. These two bands disappear along with the appearance of a new band at 1429 cm−1, when deuterated alumina is pretreated at 400°C and subsequently subjected to ammonia. This new band at 1429 cm−1 is due to NH3D+ formed from ammonia adsorbed on acidic OD sites. Consequently, ammonia IR results demonstrate the existence of Brønsted acid sites on alumina pretreated at 400°C.

ChemInform Abstract: Analysis of the High‐Resolution Spectrum of Ammonia (14NH3) in the Near‐IR Region, 6400‐6900 cm‐1.

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The rovibrational ν2 Raman spectrum of ammonia: a comparison of theory and experiment

A Raman spectrum of NH3 has been measured between 815 and 1100 cm−1 in a cell at room temperature. The rotationally and inversionally resolved spectrum and depolarization ratios are compared with purely ab initio results. These are obtained from self-consistent field calculations, corrected for correlation effects by the second-order Møller-Plesset method, and an ensuing solution of a 5-dimensional nuclear motion problem (including rotations).

Analysis of the High-Resolution Spectrum of Ammonia (14NH3) in the Near-Infrared Region, 6400-6900 cm−1

The near-infrared absorption spectrum of 14NH3 covering the 6400-6900 cm−1 region has been obtained at a resolution of 0.005 cm−1 using a Fourier transform spectrometer. The spectrum is very complex, with many squeezed or blended lines which cannot be resolved even by Doppler-limited spectroscopy. A total of 1710 lines have been observed, and 381 rotational-vibrational transitions have been assigned to the combination band v1 + v3 and the overtone band 2v3.

Lateral interactions between ammonia molecules adsorbed on titania (rutile) studied by2H NMR

The unusual transformation of the ambient temperature 2H NMR spectra of ammonia on titania (rutile), from solid state to motionally averaged singlet type with increasing surface coverage in the submonolayer regime, is attributed to the action of the repulsive lateral interaction of the molecules in the adsorbed state. The conclusions are substantiated by a new interpretation of published data.

New laboratory measurements on ammonia's inversion spectrum, with implications for planetary atmospheres

Microwave spectral measurements have been performed on pure room‐temperature gaseous ammonia at frequencies from 1.75 to 18 GHz (1.7–17 cm), at 50‐, 100‐, and 300‐torr pressures. These measurements are part of a laboratory program to measure the microwave absorption spectrum of ammonia, under conditions applicable to giant planet atmospheres, now in progress at the Jet Propulsion Laboratory. The pure ammonia data reported here agree well with previous data by Bleaney and Loubser (1950) at 100 and 300 torrs, and with predictions of the absorptivity formalism published by Berge and Gulkis. Success with pure ammonia but failure with mixtures of ammonia in hydrogen and helium (Spilker, 1990) indicates that the Berge and Gulkis formalism does not correctly handle foreign‐gas effects on ammonia inversion lines. This may require modifying conclusions of radio astronomical and radio occultation studies that used this formalism. Notably, a suggested depletion of ammonia and superabundance of hydrogen sulfide may have been exaggerated as a result of inaccuracies in the Berge and Gulkis formalism.