Electric anharmonicity in XY3 pyramidal molecules: The dipole moment function of 14NH3 and 15NH3

This paper is concerned with the determination of the shape of the electric dipole moment function of a pyramidal XY₃ molecule with a low barrier to inversion over a wide range of values for the inversion coordinate. The effective inversion-rotation Hamiltonian [V. ?pirko, J. M. R. Stone, and D. Papou?ek, J. Mol. Spectrosc.60, 159–178 (1976)] is used to explain the anomalous vibrational dependence of the electric dipole moment of ¹⁴NH₃ [F. Shimizu, J. Chem. Phys.52, 3572–3576 (1970)], and of ¹⁵NH₃ [B. J. Orr and Takeshi Oka, J. Mol. Spectrosc.66, 302–313 (1977)]. The experimental data of Orr and Oka are used to fit the μ_z component of the total dipole moment function and the fitted function is used to predict the transition moments in the nν₂ inversion sequence of ¹⁴NH₃ and ¹⁵NH₃. To illustrate the measure of the rotational dependence of the transition moments, two examples, involving ground and excited (v₂ = 1) states, are also presented.     

The ν4 state inversion spectra of 15NH3 and 14NH3

The frequencies and assignments of 45 inversion transitions of ¹⁵NH₃ and 15 additional inversion transitions of ¹⁴NH₃ in the ν₄ state are reported. The J = 0 inversion frequency and K-type doubling constant for K,l = 2, ?1 are 31 602.72 MHz and 2.000 MHz for ¹⁵NH₃. The expression containing the effective l-type doubling constant, q₀ - 5q_J - Δη…, is calculated from the (J,K,l) = (1,1,1), (1,1,?1), (2,1,1), and (2,1,?1) transitions as 10 166.022 MHz. The contribution to this expression from the Coriolis coupling with 2ν₂ is estimated for ¹⁴NH₃.     

High-resolution infrared and microwave spectroscopy of the ν4 and 2ν2 bands of 14NH3 and 15NH3

More than two thousand Stark resonances of the ν₄ and 2ν₂ band transitions of ¹⁴NH₃ and ¹⁵NH₃ were observed at Doppler-limited resolution with a CO laser. Fourier transform infrared spectroscopy on ¹⁵NH₃ is also carried out. Thirty-six new microwave transitions including seven perturbation-enhanced transitions are observed in the v₄ = 1 excited vibrational state of ¹⁴NH₃ and ¹⁵NH₃. Accuracies of all available spectroscopic data on the v₄ = 1 and the v₂ = 2 states are evaluated and analyses of the vibration-rotation spectra are performed. The Coriolis interaction between the closely lying v₄ = 1 a (antisymmetric level) and v₂ = 2 s (symmetric level) states is explicitly included in the analysis. Smaller Coriolis interactions between the v₄ = 1 a and the v₂ = 1 s states and between the v₂ = 2 s and the v₂ = v₄ = 1 a states (i.e., (v₁, v₂, v′₃, v′₄) = (0 1 0⁰ 1¹)) are also taken into consideration. The accuracy in determination of the principal molecular constants is 10^?6. The parameters thus obtained reproduce the frequencies of the vibration-rotation transitions and inversion transitions within the accuracy of 0.0024 cm^?1.     

Lorenz-type chaotic pulsing of a 15NH3-laser

The dynamics of the ¹⁵NH₃ laser operating on the v₂ = 1; aR (4, 4) rotational transition at 153 μm is investigated experimentally. Self pulsing with period doubling and chaos is observed along with periodic windows. For resonant tuning, pulsing as expected for the Lorenz case is found. Phase space projections of the Lorenz type pulsing are given. All observations agree with the predictions of the Lorenz equations extended to allow for detuning.     

Absorption measurements using CW MIR NH3 laser

The intensity and half-widths of the v₂ [sP(7,0)] line of ammonia have been measured using an optically pumped CW NH₃ laser. The influence of buffer gas is reported.     

Infrared-microwave two-photon spectroscopy of the ν2 band of 14NH3

Transitions in the ν₂ band of ¹⁴NH₃ were recorded by means of an infrared laser microwave two-photon spectrometer. The spectrometer, which uses a minicomputer to step the microwave frequency and record the spectrum, is described. With sample cells outside the laser cavity good lineshapes are obtained, so that the accuracy of frequency measurement was limited by the resettability of the CO₂ or N₂O lasers employed, ～0.0002 cm^?1. The present data are compared to previously obtained results based on CO₂ or N₂O laser frequencies and to recently reported calculations. Rotational constants derived for the hypothetical inversion-free ground and v₂ = 1 states are reported.     

High-power,line-tunable14NH3 and15NH3 lasers

A high-power, line-tunable NH₃ laser pumped by a TEA CO₂ laser has been developed for application to laser isotope separation of tritium. Laser lines from¹⁵NH₃ are newly observed in a range from 11.24 to 13.23 m. The performance of an¹⁵NH₃ laser is compared to that of an¹⁴NH₃ laser.     

High resolution diode laser measurements on the ν2 bands of 14NH3 and 15NH31

More than 500 lines in the ν₂ bands of ¹⁴NH₃ and ¹⁵NH₃ have been measured in the region 740–1200 cm^?1 with a diode laser spectrometer, with an accuracy better than 0.0005 cm^?1 for most of the lines. Wavenumbers (in cm^?1) were determined using a 3-in. Ge etalon for calibration and OCS, N₂O, NH₃, and CO₂ lines as references. The diode laser data were combined with pure inversion and inversion rotation frequencies and sets of rotational constants were obtained by the method of merged least squares. Perturbations between the Δk = ±3 levels have been taken into account in these calculations.     

Absorption spectra of NH4MnCl3 and NH4MnF3

The absorption spectra of NH₄MnCl₃ and NH₄MnF₃ crystals have been measured down to 10 K in the 250 to 600 nm region. The observed bands are assigned to electronic transitions from the ⁶A_1g(S) ground state to various excited levels of Mn²⁺ ions in an octahedral crystalline field. The position of the bands have been fitted within the strong crystal field scheme. Resulting parameters at room temperature are B=741, C=2990 and Dq=520 cm⁻¹ for NH₄MnCl₃ and B=800, C=3139 and Dq=694 cm⁻¹ for NH₄MnF₃. At low temperature some bands show a rich fine structure in which some phonon progressions have been identified.     

Vibration-inversion-rotation spectra of ammonia: Centrifugal distortion, Coriolis interactions, and force field in NH3, NH3, ND3, and NT3

An effective inversion-rotation Hamiltonian has been developed for NH₃ which avoids the necessity of having to include high powers of the inversion motion coordinate in the Taylor expansions of the potential energy and the inverse moment of inertia tensor. This nonrigid bender Hamiltonian describes the centrifugal distortion and the Coriolis interactions in the ground and excited inversion states. It also describes the inversion doublings in the ground and excited vibration-inversion states of ammonia. A least-squares procedure that includes the numerical integration of the Schrödinger wave equation has been used to determine the harmonic force field and the double-minimum inversion potential function for (¹⁴NH₃, ¹⁵NH₃) and for (¹⁴ND₃ and ¹⁴NT₃).The anomalous rotational dependence of the inversion doublings in the (±l) components of the v₄ = 1 state of ¹⁴NH₃ has been explained by the Coriolis interactions between v₂=1, v₄ = 1, v₂ = 2, v₂ = 1, v₄ = 1, and v₂ = 3 vibration-inversion states.     

81Br NQR Study of [NH3(CH2) n NH3]CdBr4 (n = 4 and 5) and [NH3(CH2) n NH3]ZnBr4 (n = 5 and 6)

⁸¹Br NQR frequencies and differential scanning calorimetry (DSC) were measured as a function of temperature. [NH₃(CH₂)₄ NH₃]CdBr₄ (1) and [NH₃(CH₂)₅NH₃]CdBr₄ (2) showed a doublet and quartet ⁸¹Br NQR spectrum, respectively. [NH₃(CH₂)₅NH₃]ZnBr₄ (3) and [NH₃(CH₂)₆NH₃]ZnBr₄ (4) exhibited a four-line ⁸¹Br NQR spectrum. From the NQR results, it is inferred that (1) and (2) consist of infinite two-dimensional sheets of corner-sharing CdBr₆ octahedra, whereas (3) and (4) have isolated [ZnBr₄]²⁻ tetrahedra. All of the crystals except (1) showed at least one structural phase transition above 380 K.     

Spectroscopic line parameters of NH3 and PH3 in the far infrared

NH₃ and PH₃ rotation and rotation-inversion line parameters in the far to medium i.r. are calculated for remote sounding purposes of planetary atmospheres; 1607 lines of ¹⁴NH₃, 362 lines of ¹⁵NH₃ and 325 lines of PH₃ are compiled. The absolute intensity formulation has been reviewed in the case of rotation adn rotation-inversion lines of molecules with C_3v symmetry. The justification of the general agreement between the authors, and comparisons with other published expressions are given.     

Br NQR relaxation and successive phase transitions of CH3NH3HgBr3

The measurement of ⁸¹Br NQR in CH₃NH₃HgBr₃ has been carried out in the temperature range between 80 and 300 K using a pulse NQR method. The temperature dependence of ⁸¹Br NQR frequencies in CH₃NH₃HgBr₃ has revealed that it undergoes three characteristic successive phase transitions at T?=?123, 184 and 239 K. The phase transition temperature at T?=?239 K is the second-order type, whereas those at T?=?184 and 123 K are the first-order nature of the phase transitions. Each phase transition seems to be closely related to the motions of methyl ammonium cation as a partial or whole. The enhancement of 1/T ₁ at T?=?239 K indicates the onset of the molecular motion of the cation as a whole with increasing temperatures.     

Theory of electronic structure and nuclear quadrupole interactions in the BF3–NH3 complex and methyl derivatives

Magnetic Hyperfine and Nuclear Quadrupole Interactions (HFI and NQI) are now important tools for characterization of systems of interest in materials research and industry. Boron-Trifluoride is an inorganic compound that is very important in this respect as a catalyst in chemical physics research and industry, forming complexes in the process with compounds like ammonia, water and methyl alcohol. The present paper deals with the BF₃–NH₃ complex and methyl derivatives BF₃NH_x(CH₃)_3?x for which we have studied the electronic structures, binding energies, and ¹⁹F* (I?=?5/2) nuclear quadrupole interactions using the first-principles Hartree–Fock–Roothaan procedure combined with electron correlation effects. Our results for the ¹⁹F* nuclear quadrupole coupling constant (e ² qQ/h) in units of MHz compare well with experiment. Trends in the binding energies and NQI parameters between the complexes are discussed.     

CH3NH3 + as a quantum and classical rotor

Spin-lattice relaxation time T ₁ is determined for protons in three polycrystals (CH₃NH₃)₅Bi₂Cl₁₁, (CD₃NH₃)₅Bi₂Cl₁₁ and (CH₃ND₃)₅Bi₂Cl₁₁. The temperature dependence of the relaxation times obtained for (CH₃NH₃)₅Bi₂Cl₁₁ and (CD₃NH₃)₅Bi₂Cl₁₁ are interpreted as a result of correlated motions of the three-proton groups of the monomethylammonium cation. ²H NMR lines of (CD₃NH₃)₃Sb₂Br₉ have been recorded between 5 K and 291 K using solid echo method. The ²H NMR line shape analysis shows that characteristic shape of tunnelling methyl group appears at about 25 K and coming down with temperature up to 5 K is more distinct. From theoretical calculation, it has been found that in the quadrupolar constants is 161.3 kHz and tunnelling frequency is above 3 MHz.     

Study on charge transfer interaction and valence state of layered perovskite-type mixed valence complex [NH3(CH2) n NH3]2[(AuII2)(AuIIII4)(I3)2] (n = 7, 8), by means of 197Au Mössbauer spectroscopy

Cs₂[Au^I X ₂][Au^III X ₄](X = Cl, Br, and I) is well known for the three-dimensional perovskite-type gold mixed valence system. Recently, layered perovskite-type gold mixed valence complexes, [NH₃(CH₂) _n NH₃]₂[(Au^II₂)(Au^IIII₄)(I₃)₂] (n = 7 and 8), have been synthesized. We have investigated the relationship between the structural dimensionality and the Au^I–Au^III charge transfer interaction for Cs₂[Au^II₂][Au^IIII₄] and [NH₃(CH₂) _n NH₃]₂[(Au^II₂)(Au^IIII₄)(I₃)₂] (n = 7 and 8) by means of ¹⁹⁷Au Mössbauer spectroscopy.     

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.     

Experimental study of the energy dependence of the reaction rate coefficients of the reaction CH 3 + with N2O and NH3

The kinetics of the reaction of CH ₃ ⁺ ions with N₂O and NH₃ has been investigated in He and Ar buffers using Selected Ion Flow Drift Tube technique (SIFDT). Both studied reactions proceed with nearly collisional rate at near thermal energies. The rate coefficient of the reaction of CH ₃ ⁺ with N₂O is decreasing more than one order of magnitude (from 1.2×10^?9cm³s^?1 up to 8×10^?11cm³s^?1) with reactant ion/reactant neutral average centre-of-mass kinetic energy (E _r) increasing from near thermal up to 2 eV. The dominant product of this reaction is the isomer HCO⁺ (≥94%) and the minor product is CH₃O⁺. The reaction of CH ₃ ⁺ with NH₃ has two binary channels with the dominant product ion CH₂NH ₂ ⁺ (>70%) and the minor product ion NH ₄ ⁺ (≈10%) and three body association channel with product CH₃NH ₃ ⁺ (≈20% at 0.32 Torr). The rate coefficient of this reaction is decreasing nearly by one order of magnitude with increasingE _r from near thermal up to 0.8eV, forE _r>0.8 eV the rate coefficient increases with increasingE _r. The experimental results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived collision complexes.     

Low temperature differential magnetization of Ni(ClO4)26NH3 and Ni(BF4)26NH3

The differential magnetization of Ni(ClO₄)₂6NH₃ and Ni(BF₄)₂6NH₃ was measured as a function of temperature (20 to 0.3 K) and magnetic field (up to 40kOe). An antiferromagnetic transition was found at T_N = 0.45 K for the Ni(ClO₄)₂6NH₃ and T_N = 0.43 K for the Ni(BF₄)₂6NH₃, and a portion of the magnetic phase diagram was determined. The interpretation of the data in terms of a uniaxial model yielded (D/k) ～ 0.2 K for both salts.