Rotational analysis of the ν2 band of NH2D

High-resolution diode laser spectra and medium-resolution F-T spectra of deuterated ammonia have been obtained in the 700- to 1030-cm⁻¹ region. Out of about 800 lines measured by diode laser spectroscopy, approximately 500 lines have been assigned to the ν₂ transitions of NH₂D. The parameters for the ground and ν₂ states of NH₂D have been derived by the simultaneous analysis of the infrared and microwave data. The standard deviation for the IR data is ∼8 × 10⁻⁴ cm⁻¹. It is shown that the energy levels of NH₂D in the ν₂ state are heavily perturbed by inversion-rotation interaction and that it is necessary to include higher order inversion-rotation interaction terms to obtain a satisfactory fit of the observed data.     

Inversion-rotation interaction in NH2D: Intensity perturbations in the ν2 band

The parameters of NH₂D in the ground and ν₂ states have been refined by a simultaneous analysis of the microwave, FTIR, and diode laser data. The intensities of 46 NH₂D lines have been measured, and from a least-squares fit of the intensity data the a ← s, s ← a, s ← s, and a ← a transition moments have been derived. The intensities of the lines in the ν₂ band of NH₂D have been calculated taking into account the inversion-rotation interaction. The accuracies of the wavenumbers and intensities calculated with the new parameters are estimated to be better than ±0.0002 cm⁻¹ and ±5%, respectively. The matrix elements for interaction of vibrations through x, y, and z axis couplings are appended.     

Inversion and inversion-rotation spectrum of 14NH3 in the ν2 excited state

Using the vibration-inversion-rotation Hamiltonian for ammonia [V. ?pirko, J. M. R. Stone, and D. Papou?ek, J. Mol. Spectrosc.60, 159–178 (1976)], a modified theory is worked out for the Δk = ±3n interactions between the inversion-rotation energy levels of NH₃ which takes into account the large amplitude inversion motion. Eighty frequencies of inversion and inversion-rotation transitions and two perturbation-allowed transitions in the ν₂ state of ¹⁴NH₃ are measured in the far-infrared region around 1 THz (≈33 cm^?1), mostly with the microwave accuracy, by the radiofrequency spectrometer with acoustic detector. By a least-squares fit of these data and the data of the infrared-microwave two-photon and infrared heterodyne measurements of the ν₂ band, a set of molecular constants for the ν₂ state of ¹⁴NH₃ is obtained which reproduces the submillimeterwave data with the accuracy of the experiment.     

Electron paramagnetic resonance and spin-lattice relaxation in two-dimensional systems

The anisotropies of the EPR linewidth andg-factor were investigated in two-dimensional molecular composites of the type [NH₃?R?NH₃]MX₄. Measurements were performed both in single crystals and powders over the temperature range 4.2–290 K. The spin-lattice relaxation timeT ₁ was measured using the modulation method, as a function of temperature. The samples exhibit different structures and coupling interactions, according to the nature of the halogen X, the metal M and the organic radical R. We have analysed the influence of these parameters on spin behavior by studying the samples [NH₃?(CH) _n ?NH₃]MX₄ with M=Mn, Cu; X=Cl, Br, andn=2, 3, 4, 5. When R is constituted by molecules with unsaturated bonds, these materials can be considered as excellent matrices for selective polymerisation reactions by irradiation or thermal processing. We have performed EPR measurements on the heated complex of propargylamine and cadmium chloride [HC∈C?CH₂?NH₃]₂CdCl₄. The obtained data are interpreted taking into account the strong exchange interaction and the various coupling interactions in the samples. The thermal dependences ofT ₁ are explained by means of the Bloembergen and Wang three-reservoir model. The data whow spin diffusion when the metal is manganese, and an antisymmetric exchange interaction modulated by phonons in the case of copper. The nature of the halogen plays an important role in spin dynamics and namely in spin-lattice relaxation. The results obtained on [HC∈C?CH₂?NH₃]₂CdCl₄ after heating under vaccum show the creation of many paramagnetic centers due to the vanishing of triple bonds and the occurrence of a strong exchange interaction.     

Millimeter- and submillimeter-wave length spectrum of the partially deuterated ammonias; A study of inversion,centrifugal distortion,and rotation-inversion interactions

Eighty-two new rotation-inversion transitions of the light asymmetric rotors NH₂D and ND₂H have been measured in the 80–600 GHz region by means of high resolution microwave techniques. Included among these transitions are several submillimeter R-branch transitions which make possible a calculation of both the rotational and distortion parameters which characterize the molecule. An accurate inversion Hamiltonian is developed and used as a preliminary step to a rotation-distortion treatment of the molecule. The spectrum of ND₂H reveals the existence of a rotation-vibration interaction which significantly alters the energy of a number of ground vibrational state levels. The results of an analysis technique which incorporates the effects of this perturbation as well as the inversion effects are presented. This procedure makes possible the analysis of all observed transitions to within experimental uncertainties as well as the accurate prediction of unobserved transitions. The rotational constants which result from this work are (MHz): For NH₂D, O⁺ vibrational state,a= 290 286.53 ± 0.21,B= 192 240.15 ± 0.42,C= 140 602.50 ± 0.42; for NH₂D, O^? vibrational state,a= 290 192.14 ± 0.21,B= 192 176.27 ± 0.42,C= 140 625.64 ± 0.42; for ND₂H, O⁺ vibrational state,a= 223 222.92 ± 0.18,B= 160 433.96 ± 0.17,C= 112 305.40 ± 0.17; for ND₂H, O^? vibrational state,a= 223 147.21 ± 0.14,B= 160 423.37 ± 0.13,C= 112 313.72 ± 0.13.     

The inversion potential for NH3 and its isotopic species

Usingab initio data of the potential surface for the ground state of NH₃ a function is obtained to represent, with a very high precision, the potential along the inversion coordinate. The inversion spectra of NH₃, ND₃, NH₂D and NHD₂ are found by numerically solving the Schrödinger equation for this potential. Comparison is made of the calculated inversion frequencies and the experimental values, and the molecular constants of NH₃ are also compared to those found in the literature.     

Rotational Spectra of CH3CCH–NH3, NCCCH–NH3, and NCCCH–OH2

Microwave spectra of NCCCH–NH₃, CH₃CCH–NH₃, and NCCCH–OH₂have been recorded using a pulsed-nozzle Fourier-transform microwave spectrometer. The complexes NCCCH–NH₃and CH₃CCH–NH₃are found to have symmetric-top structures with the acetylenic proton hydrogen bonded to the nitrogen of the NH₃. The data for CH₃CCH–NH₃are further consistent with free or nearly free internal rotation of the methyl top against the ammonia top. For NCCCH–OH₂, the acetylenic proton is hydrogen bonded to the oxygen of the water. The complex has a dynamicalC_2vstructure, as evidenced by the presence of two nuclear-spin modifications of the complex. The hydrogen bond lengths and hydrogen-bond stretching force constants are 2.212 Å and 10.8 N/m, 2.322 Å and 6.0 N/m, and 2.125 Å and 9.6 N/m for NCCCH–NH₃, CH₃CCH–NH₃, and NCCCH–OH₂, respectively. For the cyanoacetylene complexes, these bond lengths and force constants lie between the values for the related hydrogen cyanide and acetylene complexes of NH₃and H₂O. The NH₃bending and weak-bond stretching force constants for CH₃CCH–NH₃are less than those found in NCCCH–NH₃, NCH–NH₃, and HCCH–NH₃, suggesting that the hydrogen bonding interaction is particularly weak in CH₃CCH–NH₃. The weakness of this hydrogen bond is partially a consequence of the orientation of the monomer electric dipole moments in the complex. In CH₃CCH–NH₃the antialigned monomer dipole moments lead to a repulsive dipole–dipole interaction energy, while in NCH–NH₃and NCCCH–NH₃the aligned dipoles give an attraction interaction.     

Magnetic susceptibility studies of (CH2)3(NH3)2FeCl2Br2 and (CH2)6(NH3)2FeCl2Br2

The magnetic susceptibility of the layered compounds (CH₂)₃(NH₃)₂FeCl₂Br₂ and (CH₂)₆(NH₃)₂FeCl₂Br₂ has been measured in the range 80 < T < 300 K. The results follow a Curie-Weiss behavior in the range 120 < T < 300 K but are field dependent for T < 120 K. The results are interpreted in terms of a two-dimensional antiferromagnetic interaction which is canted. A comparison with the corresponding pure chloride compounds is given.     

High-J transitions in the ν2 bands of 14NH3 and 15NH3

The Fourier transform spectra measured using the multiple reflection absorption cell with a path length of 192 m are reported for the high-J transitions of the ν₂ bands of ¹⁴NH₃ and ¹⁵NH₃. More than 400 transitions which have been assigned for the first time in both ¹⁴NH₃ and ¹⁵NH₃ represent nearly 100% extension of the ν₂ data.     

The microwave spectrum,structure, and dipole moment of amino acetonitrile

The microwave spectra of three isotopic species of amino acetonitrile (NH₂CH₂CN, NHDCH₂CN, and ND₂CH₂CN) have been investigated to learn something about the structure and bonding in this and similar compounds. The only rotamer observed is the form in which both NH bonds are gauche to the CN group and the structure is quite rigid. From the available data only the bond angles are well determined. The amino NCC angle is 114.5(3)°, the HCH angle is 103(2)°, the HNC angle is 109.6(4)°, and the HNH angle is 107(1)°. The dipole moment components are μ_a = 2.577(7) D and μ_b = 0.5754(10) D; these agree quite well in magnitude and direction with the sum of the acetonitrile and methyl amine dipoles. The rigidity of the molecule and its preference for the form in which the amino protons are closest to the triple bond confirms a suggestion based on earlier studies on similar molecules that there is a strong hydrogen bonding interaction between the amino group and the nitrile group, although in this molecule dipole-dipole forces also probably play a significant role in determining the structure and its rigidity.     

Two dimensional NQR separation of inhomogeneous and homogeneous lineshapes in disordered solids

A two-dimensional (2D) zero field NQR separation of inhomogeneous and homogeneous lineshapes technique is described. The nuclear spin Hamiltonian for spinsI>1/2 in zero magnetic field consists to a good approximation only of the electric quadrupole term. The 2D separation technique enables a separate spectroscopic observation of a static and a randomly time-fluctuating dynamic part of the quadrupole interaction. The separation is based on the fact that nuclear spin precession under a static quadrupolar Hamiltonian can be time-reversed whereas this can not be achieved under the action of a randomly time-fluctuaing Hamiltonian. The 2D spectrum displays in theω ₂-domain the inhomogeneously broadened lineshape, which is a convolution of the inhomogeneous static frequency distribution function and the homogeneous (adiabatic) lineshape. Theω ₁-domain shows the pure homogeneous lineshape. A deconvolution of the inhomogeneous lineshape with the homogeneous one yields a pure static inhomogeneous frequency distribution function which is characteristic and theoretically known for many different models of disordered solids like glasses and incommensurate systems. This technique is important in studies where both lineshapes have comparable widths. The 2D NQR separation technique has been applied to⁷⁵As in a proton glass Rb_0.98(NH₄)_0.02H₂AsO₄.     

Magnetic susceptibilities of polycrystalline samples of the compounds ANiCl3 (A = RB,NH4, Tl,Cs) and ANiBr3 (A = Rb,Cs)

The susceptibilities of polycrystalline samples of various antiferromagnetic linear-chain compounds ANiX₃ (A =Tl, NH₄, Rb, Cs and X = Cl, Br) have been measured in the temperature region 2–200 °K. The results, amongst which the already known data for RbNiCl₃ and CsNiCl₃, are interpreted in terms of a theory, developed by Weng, for antiferromagnetic Heisenberg linear-chain systems with spin S = 1. By means of Oguchi's Green function theory and the experimentally determined transition temperatures T_N the order of magnitude of the ratio between inter- and intra-chain interaction is obtained.     

Shock tube study of the interaction between ammonia and nitric oxide at high temperatures using laser absorption spectroscopy

The interaction between ammonia (NH₃) and nitric oxide (NO) at high temperatures is studied in this work using a shock tube combined with laser absorption diagnostics. The system simultaneously measured the NH₃ and NO time-histories during the reaction processes of the shock-heated NH₃/NO/CO/Ar mixtures (NH₃:NO ≈ 0.9:1.0 and 1.4:1.0). The absorption cross-sections of NH₃ near 1122.10 cm^–1 and NO at 1900.52 cm^–1 (characterized in this study) were used for measuring NH₃ and NO time-histories with the temperature measured by two CO absorption lines. The measured NH₃ and NO time-histories at 1614–1968 K and 2.4–2.8 atm were compared with predictions of seven recent kinetics models. The predictions that based on different mechanisms are very different and the measured profiles are within the range of the predictions. The Glarborg, NUI Galway Syngas-NOx, and Mathieu mechanisms give the closest predictions to the measurements. Kinetics analyses indicate that the NH₃ and NO consumption rates are extremely sensitive to the rate constants and branching ratio of NH₂ + NO = N₂ + H₂O and NH₂ + NO = NNH + OH, which are more reliably represented in the Glarborg and NUI Galway Syngas-NOx mechanisms. The performances of Glarborg mechanisms at lower initial temperatures can be apparently improved by revising the rate constants and branching ratio of NH₂ + NO = N₂ + H₂O and NH₂ + NO = NNH + OH. These two reactions are also the primary pathways for NO reduction and NH₃ is mainly consumed via NH₃ + OH = NH₂ + H₂O and NH₃ + H = NH₂ + H₂. Trace amounts of NO₂ and N₂O impurities decompose to form O radical followed by the generation of OH radical via H-abstraction reactions, which significantly affects the predictions of NH₃ and NO according to kinetics analyses.     

The 5νNH and 5νND vibrational bands of partially deuterated ammonia species

Absorption spectra of gaseous samples containing NH₂D and NHD₂ have been measured in the 11 580-11 880 and 15 280-15 610 cm⁻¹ regions, corresponding to the 5ν_ND and 5ν_NH vibrational bands, respectively. Photoacoustic spectroscopy has been utilized for the measurement. The molecular constants of NH₂D in the 5ν_ND state and NHD₂ in the 5ν_NH state have been determined from the analysis of the obtained absorption spectrum. From the comparison of the constants with those of the vibrational ground states, structural changes caused by the stretching excitations have been elucidated. The HND bond angles are decreased by these excitations. The dependence of the molecular constants on the stretching quantum number has also been derived by simple Birge-Sponer and Dunham analyses.     

RAIRS investigations on the orientation and intermolecular interactions of adenine on Cu(1 1 0)

The adsorption of the DNA base adenine (C₅N₅H₅) on Cu(1 1 0) has been investigated as a function of coverage and temperature using reflection absorption infrared spectroscopy. These data provide important information on the nature of the local adsorbed complex and the intermolecular lateral interactions that come into play at high coverages. The RAIR spectra are consistent with an adsorption geometry in which the molecular ring is substantially tilted from the surface plane and in which the two amino hydrogens are equidistant from the surface, thus rationalising the appearance of a very strong βNH₂ scissoring mode, along with the activity of in-plane vibrational modes and the observation of the symmetric ν_symNH₂ stretch, but not the asymmetric ν_asymNH₂ stretch. In addition, coordination to the metal surface is proposed to occur at the N(9) position with a possible additional interaction through the N(3) position, both of which are the favoured coordination points in the metal complexes of adenine. This is a strong interaction and leads to a highly stable adsorbed layer. Our data also provide the first direct evidence of hydrogen bonding in the adlayer as coverage is increased, attributed to interactions between the amino group of one molecule and the N(1) and N(7) positions of a neighbouring species. When adsorption is carried out at room temperature, a very heterogeneous adlayer is created in which a diversity of molecular aggregates co-exist. However, upon annealing, a more ordered hydrogen bonded adlayer is formed in which one type of hydrogen bonding assembly is preferred. Finally, we propose that the hydrogen bonded assemblies created at a surface probably involve bent hydrogen bonds which arise from a compromise between the strong molecule-metal interactions that orientate the molecule and weaker lateral hydrogen bonding interactions that dictate the two-dimensional architecture.     

Millimeter-wave spectroscopy of the weakly bound molecular complex NH3-N2

The rotational spectrum of the van der Waals NH₃-N₂ complex is studied in the frequency range of 112?C130 GHz. The transitions are measured in a cold molecular beam with an intracavity spectrometer based on an orotron. A total of six new transitions of different spin modifications of the complex are recorded. Molecular parameters of the K = 0 ground state are determined for the orthoNH₃-orthoN₂ modification.     

Phase situation in ferroelectric NH4HSeO4 crystals with various degrees of deuteration

NH₄HSeO₄ crystals of varying deuterium content have been studied. The high-temperature phase transition at 408 K is observed both for crystals of symmetry I2 grown from the solutions containing 0–40% D and those of symmetry P2₁2₁2₁ i.e. grown solutions containing above 50% D. This phase transition practically does not depend on %D. For the crystals of symmetry P2₁2₁2₁ an additional dielectric anomaly at 338 K (only slightly dependent on %D) has been found which most probably should be assigned to the P2₁2₁2₁-I2 transition. The results obtained and our earlier data available so far enabled to construct more detailed phase diagram for NH₄HSeO₄ with %D as a parameter.     

Magnetic transitions in NiBr2 6NH3 and NiCl2 6NH3 up to 75 koe

The field dependence of the magnetic susceptibility of powdered NiBr₂ 6NH₃ and NiCl₂ 6NH₃ was measured up to 75 koe at temperatures above and below T_N. The anomalies found are discussed in terms of other magnetic data known for these salts.     

Characterizing ammonia and nitric oxide interaction with outwardly propagating spherical flame method

With the growing attention on ammonia (NH₃) combustion, understanding NH₃ and nitric oxide (NO) interaction at temperatures higher than DeNOx temperature region or even flame temperature becomes a new research need. In this work, the outwardly propagation spherical flame method was used to investigate the laminar flame propagation of NH₃/NO/N₂ mixtures and constrain the uncertainties of the specific kinetics. The present experiments were conducted at initial pressure of 1 atm, temperature of 298 K and equivalence ratios from 1.1 to 1.9. A kinetic model of NH₃/NO combustion was updated from our previous work. Compared with several previous models, the present model can reasonably reproduce the laminar burning velocity data measured in this work and speciation data in literature. Based on model analyses, the interaction of NH₃ and NO was thoroughly investigated. As both the oxidizer and a carrier of nitrogen element, NO frequently reacts with different decomposition products of NH₃ including NH₂, NH and NNH, and converts nitrogen element to the final product N₂. It is found that the laminar burning velocity experiment of NH₃/NO/N₂ mixtures using the outwardly propagating spherical flame method can provide highly sensitive validation targets for the kinetics in NH₃ and NO interaction.     

Collision induced transitions of ammonia calculation of relaxation timesT 1 andT 2, line widths,line shifts,and the double resonance effect

The longitudinal relaxation timeT ₁ and the transverse relaxation timeT ₃ for the inversion levels of the NH₃ molecule have been calculated for NH₃ — NH₃, NH₃ — N₂ and NH₃ — H₂ collisions. The ratioT ₂/T ₁ lies between 1 and 2 which agrees well with the experiment. The phase shift effect onT ₂ and on the collisioninduced line shift δω under the framework of the Mehrotra-Boggs theory have also been evaluated. The change in the line intensity ΔI/I, in four-level double resonance experiments was also calculated, and the significance of higher order interaction terms has been pointed out.