Hyperfine structure,mm wave rotational spectrum and molecular constants of the diatomic IF in its electronic ground stateX 1 Σ+

At wavelengths near 1 mm the rotational transitionsJ=16←15 and 17←16 of the diatomic IF have been observed. The strong hyperfine transitions ΔF=+1 were measured in vibrational statesv=0, 1 and 2. The much weaker ΔF=0 components could be detected in the rotational transitionJ=17←16 of the molecule in its ground vibrational state. The analysis including previous measurements at larger wavelengths resulted in improved hyperfine parameters, an extended set of Dunham energy coefficients and potential constants.     

The production of Te atoms by the multiphoton dissociation of diethyltelluride

Detection of Te atoms in the ground ³P^2,1,0 states has been accomplished using two-photon laser-induced fluorescence (LIF) and “2 + 1” multiphoton ionization (MPI). Te atoms were produced by multiphoton dissociation of (C₂H₅)₂Te in the region 358–395 nm. The LIF and MPI experiments utilize selective excitation of the 6p ³P_J′←5p ³P_J″ and 7p ³P_J′←5p ³P₂ transitions by two-photon absorption. Line strength intensities for the individual J′ ← J″ fine structure pairs of the 6p ³P_J′ ← 5p ³P_J″ two-photon transitions were calculated and compared to the LIF data. Intensities of these transitions of Te atoms are compared to analogous ³P ← ³P transitions in S and O atoms.     

Avoided-crossing molecular-beam spectroscopy of CH3SiF3

The avoided-crossing molecular-beam method has been applied to CH₃SiF₃ in the ground torsional state. Stark and hyperfine rotational anticrossings have been studied, along with barrier anticrossings in which the zero-field energy differences depend only on the torsionial splittings. For υ = 0, pure rotational spectra were measured forJ = 13 ← 12 and 14 ← 13 with a mm-wave spectrometer and for J = 1 ← 0 with the molecular-beam spectrometer. Stark and Zeeman studies have been carried out with conventional beam techniques. From a simultaneous analysis of existing microwave data for υ ? 2 and the current measurements, it was found that the moment of inertia of the methyl top I_α = 3.170(2) amu A², the effective rotational constants A^eff = 4059.522(22) Mhz, and the effective height of the barrier V₃^eff = 413.979(14) cm^?1. The true values of A and V₃ have been obtained within certain approximations. The rotational constant B and several distortion constants including D_K were evaluated. In addition to determining the electric dipole moment μ 2.33938(14) D, the data yielded values for the distortion dipole constants μ_D and μ_J, and the molecular g-factors g_| and g_⊥.     

D-nuclear quadrupole coupling in the rotational spectrum of 15N2…DF and an interpretation of the hyperfine coupling constants χ aaD and DaaHF within a series of complexes B…HF

Hyperfine structure in the J = 1 ← 0 and J = 2 ← 1 transitions of ¹⁵N₂…DF, arising from D-nuclear quadrupole coupling and D, ¹⁹F nuclear-spin—nuclear-spin coupling, has been observed and measured by using pulsed-nozzle Fourier-transform microwave spectroscopy. The following rotational, centrifugal distortion and hyperfine coupling constants were determined: β_o = 3091.9004 MHz, D_J = 14.75 kHz, χ_aa^D = 278.6(38) kHz and D_aa^HF = ?38.5(38) kHz. An interpretation is presented for the variation of the coupling, constants χ_aa^D and D_aa^HF along the series B…DF and B…HF, where B = Ar, Kr, Xe, ¹⁵N₂, CO, PH₃, H₂S, HC¹⁵N and H₂O.     

Microwave spectra and dipole moments of bicyclo [2.2.1]-hepta-7-one and bicyclo [2.2.1]hept-2-en-7-one

The microwave spectra of bicycle [2.2.1] hepta-7-one (I), bicyelo [2.2.1] hept-2-en-7-one (II), and exo-5,6-bisdeuteriobicyclo [2.2.1] hept-2-en-7-one (III) have been recorded in the region between 26.5 and 40.0 GHz. The rotational constants in the order A, B, C for the title compounds are 2773.24±0.31, 2301.74±0.04, and 2133.96±0.02 (I); 2979.22±0.08, 2418.60±0.01, and 2235.51±0.01 (II); and 2789.67±0.06, 2385.24±0.01, and 2150.60±0.01 (III). The rotational constants of four vibrationally excited states were also determined for (II). Quadratic Stark effect measurements on the 7₁₆ ← 6₁₅ transition of (I) gave ¦μ_a¦=2.99±0.03. Similar measurements on two 5 ← 4 and 4 ← 3 transitions of (II) gave ¦μ_a¦=2.88±0.03, ¦μ_b¦=0.39±0.03, ¦μ_c¦=0, and ¦μ_total¦=2.91±0.04.     

cw Two-photon transitions in K2 molecular beams

We report on the two-photon visible excitation spectra of potassium molecules in a supersonic beam. A dye laser excites K₂ to different (7s ¹Σ_g, 9s ¹Σ_g, 8d ¹Δ_g) Rydberg states. Two-photon transitions are detected by monitoring the resulting (third-photon) ionization. We have made detailed studies, including rotational assignment of 92 such transitions, ¹Δ_g(v¹, J¹) ← X ¹Σ_g(v = 0, J), where the B ¹Π_u state forms the intermediate enhancing state.     

Microwave-optical double resonance in molecular ions. Co+

Microwave—optical double resonance signals have been detected in a mass-selected ion-beam spectrometer for ¹²C¹⁶O⁺. With the optical excitation of fluorescence from the R₁ ($\text{1}\text{2}$) line of the (0,0) band of the A²Π_{$\text{3}\text{2}$} ← X²∑ transition of 20350.6 cm^?1, the microwave resonances occurred at 118101.8 ± 0.2 MHz and at 117694 ± 2 MHz corresponding to the N= 1, J = $\text{3}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ and the N = 1, J = $\text{1}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ transitions.     

Millimeter wave spectrum of gaseous bismuth monofluoride (BiF)

Rotational transitions of gaseous bismuth monofluoride (BiF) have been observed for the first time. The molecules were produced in a double oven system and subsequently led into the absorption cell at a temperature of 700 °C. Transitions (F′,J + 1,v) ← (F,J,v) with J = 4,6 and 7 and v = 0–6 in the O⁺ electronic ground state have been measured in the 65–110 GHz region. The hyperfine structure due to the Bi nucleus is completely resolved. Analysis of the spectrum yields the following rotational and hyperfine constants: Y₀₁ = 6894.89594(84) MHz, Y₁₁ = ?45.0474(11) MHz, Y₂₁ = 81.69(45) kHz, Y₃₁ = 0.177(51) kHz, Y₀₂ = ?5.5440(73) kHz, eq_eQ(Bi) = ?1150.28(12) MHz, eq_IQ(Bi) = 4.20(12) MHz, c_Bi = ?30.0(5) kHz. In the Dunham constants Y_lm contribution due to interaction with 1⁺-level is included. The equilibrium distance, potential and vibrational constants are derived.     

N2 rotational energy distributions in cold,supersonic beams from electron excited fluorescence measurements of N+2

Ground-state rotational energy distributions of N₂ molecules produced in pure and He-seeded supersonic expansions have been determined by measurements of the N⁺₂ first negative band rotational line intensities produced by 800 eV electron impact on cooled pure and He-seeded N₂ supersonic beams. Sufficient spectral resolution was employed to resolve completely both P and R branches of the first negative bands. Rotational state distributions were obtained to much higher values of J than in previous investigations. The data show that at 800 eV, the electric dipole selection rule, |ΔJ| = 1, is consistent with the observed N⁺₂ emission bands and that the rotational energy distributions produced in the cooled, supersonic beam are non-Boltzmann with a large population in the first few rotational states followed by a long, high-energy fail to quite high J values.     

HF(B1Σ→X1Σ) UV chemiluminescence from the H+/H+2+F− ion-ion reactions

Chemiluminescence spectra attributable to the H⁺/H⁺₂+F⁻→ HF B¹Σ ion-ion reactions were obtained in the wavelength region 185–270 nm. The rovibrationally resolved bands were assigned as HF B ¹Σ (v', J') to HF X ¹Σ (v″,J″) transitions with 0⩽v'⩽4 and 12 ⩽ v″ ⩽ 16. The corresponding rotational branches all have peaks at high J values. These non-thermal distributions suggest that the corresponding product state v',J' populations reflect the nascent distribution from the ion-ion reactions.     

Emission spectra of Cs2NaTbCl6 and Cs2NaYCl6: Tb3+

The emission spectra of microcrystalline Cs₂NaTbCl₆ and Cs₂Na(Y_0.99Tb_0.01)Cl₆ have been measured at room temperature and at 77 K. The crystal structures of these compounds are face-centered cubic and the terbium (III) ions lie at sites of octahedral (O_h) symmetry surrounded by six chloride ions. Emission is observed from both the ⁵D₃ and ⁵D₄ excited states of Tb³⁺. Assignments have been made for nearly all of the magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions. These assignments are based on the calculated transition energies and relative magnetic-dipole strengths and intensities obtained from a weak-field crystal-field analysis of octahedral TbCl₆^3? units. Magnetic-dipole lines dominate the spectra for transitions of ΔJ = ±1 free-ion parentage, whereas both magnetic-dipole lines and vibronically induced electric-dipole lines contribute significantly to the emission intensities of the ΔJ = 0, ±2 transitions. The crystal-field sub-levels of both ⁵D₃ and ⁵D₄ appear to reach a Boltzmann thermal equilibrium prior to emission. Emission from ⁵D₃ is partially quenched in going from low temperature to high temperature and in going from Cs₂NaYCl₆: Tb³⁺ (1%) to Cs₂NaTbCl₆.This study has led to the identification and assignment of nearly all of the pure magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions in crystal-line Cs₂NaTbCl₆. The assignments were based on calculated transition energies and relative magnetic-dipole strengths (and intensities) obtained from a (weak-field) crystal-field analysis of octahedral (O_h) TbCl₆^3? clusters. Excellent agreement between the calculated and observed relative intensities of the magnetic-dipole lines was achieved by assuming a Boltzmann equilibrated set of crystal-field sub-levels for both the ⁵D₄ and ⁵D₃ emitting states. Furthermore, the experimental results suggest that ⁵D₄ ← ⁵D₃ relaxation is temperature-dependent.The energy levels calculated and displayed in table 1 appear to be qualitatively correct and are in semiquantitative agreement with the emission results (as interpreted in section 4). Calculated and observed transition energies for the assigned magnetic-dipole transitions generally agree to within 0.2%.One of the most remarkable features of the emission spectra obtained on Cs₂NaTbCl₆ is the absence of any vibrational structure in the ΔJ = ± 1 transitions (⁷F₆, ⁷F₃ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃), and the presence of extensive vibrational structure in the ΔJ = O, ±2 transitions (⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄). If other than OO vibronic transitions do contribute to the ΔJ = ±1 emissions, their intensities must be at least two or three orders-of-magnitude weaker than the OO magnetic-dipole lines. Vibronically induced electric-dipole transitions appear, however, to make substantial contributions to the ⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄ emission spectra. A clear-cut theoretical explanation for the absence of vibrational structure in the ΔJ = ±1 transitions is not readily apparent. We are presently examining this problem in greater detail.     

Rotational and hyperfine parameters of NH2(X2B1) from LMR spectra

Seventeen rotational transitions up to N=7 of the NH₂ radical in its ground vibronic state have been measured by far infrared laser magnetic resonance spectroscopy. Analysis of the Zeeman patterns and hyperfine structure yields precise rotational, spin-rotational and distortion parameters, and isotropic and anisotropic hyperfine interaction parameters for both ¹⁴N and ¹H nuclei.     

Improved flexibility in MODR using a supersonic jet source: Applications to CO+ and CN

Microwave—optical double resonance (MODR) is carried out on the N = 1 ← 0 transitions of CN and CO⁺, which are rotationally cooled in a supersonic jet. Large modulations in the probe LIF (≈100%) are observed without optical saturation, demonstrating that short pulse dye lasers may be used in MODR. Hyperfine constants for ¹²C¹⁴N in X?²Σ^?(ν = 2) are reported.     

The rotational spectra of the ground and first excited bending states of deuterium isocyanide,DNC, up to 2 THz

The pure rotational spectrum of deuterium isocyanide (DNC) was recorded in the frequency range from approximately 680 to 1985 GHz. Twenty-one new transitions in the vibrational ground and first excited bending states (01^e,f 0) have been assigned, namely R-branch transitions from J=9←8 to 25←24. In a least squares analysis of these new transition frequencies together with previously reported millimeter-wave data, spectroscopic parameters up to sextic order could be derived with high precision for both states. Furthermore, the ℓ-type doubling constant q and its centrifugal distortion terms q_J and q_JJ were obtained for the first excited bending state.     

Heterodyne laser spectroscopy of lithium ions: 23 P fine and hyperfine structure of7Li+

The fine structure (fs) splittings in the 1s2p ³ P _J=1,2,0 multiplet of the helium-like⁷Li⁺ ion were measured with a laser spectrometer. The results with 3σ errors are: Δv ₀₁ (³ P ₀,F=3/2?³ P ₁,F=5/2)=152081.6(2.0) MHz and Δv ₀₂ (³ P ₀,F=3/2?³ P ₂,F=7/2)=82704.3(1.9) MHz. Combining the new precise fs measurements with earlier hyperfine structure (hfs) results from laser-microwave spectroscopy provided improved fs constants:D ₁=?155709.0(2.1) MHz,D ₂=?93049.2(2.0) MHz, and hfs constants:A _c =3679.0(6) MHz,A ₀=51.0(4) MHz, andA _d =?11.3(1) MHz, thus allowing for a stringent test of available theoretical data. The spectroscopic method used in this work opens up the possibility of determining Li⁺, 2³ S?2³ P absolute transition frequencies with a precision of ～2·10^?9.     

Li47B3P14N42—A Lithium Nitridoborophosphate with [P3N9]12−, [P4N10]10−, and the Unprecedented [B3P3N13]15− Ion

Li₄₇B₃P₁₄N₄₂, the first lithium nitridoborophosphate, is synthesized by two different routes using a Li₃N flux enabling a complete structure determination by single‐crystal X‐ray diffraction data. Li₄₇B₃P₁₄N₄₂ comprises three different complex anions: a cyclic [P₃N₉]¹²⁻, an adamantane‐like [P₄N₁₀]¹⁰⁻, and the novel anion [P₃B₃N₁₃]¹⁵⁻. [P₃B₃N₁₃]¹⁵⁻ is the first species with condensed B/N and P/N substructures. Rietveld refinement, ⁶Li, ⁷Li, ¹¹B, and ³¹P solid‐state NMR spectroscopy, FTIR spectroscopy, EDX measurements, and elemental analyses correspond well with the structure model from single‐crystal XRD. To confirm the mobility of Li⁺ ions, their possible migration pathways were evaluated and the temperature‐dependent conductivity was determined by impedance spectroscopy. With the Li₃N flux route we gained access to a new class of lithium nitridoborophosphates, which could have a great potential for unprecedented anion topologies with interesting properties.     

Experimental and theoretical cross sections for photoionization of metastable Xe*. (6s 3 P 2, 3 P 0) atoms near threshold

Using high resolution laser photoelectron spectrometry we have determined absolute cross sections σJ ₀ J ₁ and the electron angular distribution parameter for one photon ionization of metastable Xe^*(6s ³ P _J0, J ₀ = 2, 0) atoms to the resolved Xe₊ (² P _J1, J ₁ = 3/2, 1/2) ion states at several wavelengths near threshold. For comparison with the present and future experimental data we have calculated partial cross sections and ß-parameters for photoionization of Xe^*(6s ³ P _J0, J ₀ = 2, 0) and of the analogous alkali atom Cs(6s) over the photoelectron energy range (0–5) eV. We have used both a term-dependent Pauli-Fock (PF) approach and a configuration interaction method involving Pauli-Fock atomic orbitals (CIPF). Through the PF method we include relativistic effects on the atomic orbitals; the CIPF method was designed to take into account the important electron correlation effects which are found to be essential for obtaining good agreement between the theoretical and experimental results.     

Quasi-resonant energy transfer in collisions: Na2(A1Σ u + )+K(4S)

Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na₂(A) to potassium atoms as described by Na₂(A¹Σ _u ⁺ ,v′J′)+K(4S)→Na₂ (X¹Σ _g ⁺ ,v″J″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimerv′J′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm^?1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm^?1) the cross section is Q=7.8×10^?13 cm².     

The B–N Bond in Some Aminoboranes and an Iminoborane,Studied by 11B and 15N NMR Spectroscopy and DFT Methods

¹⁵N NMR spectra of several aminoboranes (Me₂B–NMe₂, Cl₂B–NMe₂, Br₂B–NMe₂, OCH₂CH₂OB–NMe₂), three N‐pyrrolylboranes, and an iminoborane (tBu–B≡N–tBu) was measured. The spin‐spin coupling constants ¹J(¹⁵N, ¹¹B) were resolved at elevated temperatures. In the case of the iminoborane at 105 °C, the coupling constant ¹J(¹⁴N,¹¹B) = 57 Hz could also be determined from the ¹¹B NMR spectrum [from ¹⁵N NMR ¹J(¹⁵N,¹¹B) = 81 Hz]. Generally, there is no correlation between the magnitude of ¹J(¹⁵N,¹¹B) and the bond length d_BN. The values ¹J(¹⁵N,¹¹B) indicate that changes in σ bonding affect their magnitude, and the nature of the lone pair of electrons at nitrogen is of great importance. The calculated NMR parameters of an adduct of the iminoborane with an N‐heterocyclic carbene, show that the bonding situation around the BN double bond in the adduct is comparable with imines.     

The direct l-type resonance spectrum of CF3CCH in the vibrational state v10=3: Extension of the theory of reduction to H6n terms

The direct l-type resonance spectrum of CF₃CCH has been measured in the v₁₀=3 vibrational state by means of waveguide microwave Fourier transform spectroscopy in the range 8–26 GHz. Three types of direct l-type resonance transitions induced by the (Δk=Δl=±2) interaction could be observed: 140 transitions following the ΔJ=0, Δk=Δl=±2, Δ|l|=0, selection rule covering values of J=17–61 and G=|k−l| from 1 to 7, 94 transitions following the ΔJ=0, Δk=Δl=±2, Δ|l|=±2, selection rule covering values of J=26–57 and G from 15 to 24, 90 transitions following the ΔJ=0, Δk=Δl=±4 selection rule covering values of J=34–80 and G from 3 to 12 and 13 transitions following the ΔJ=0, Δk=Δl=±6, k=∓1, l=∓1⇔k=±5, l=±3 selection rule for J=71-83. 14 A₁–A₂ splitting transitions with kl=+1 were measured from J=33 to 49. Strong perturbations due to Δ(k−l)=±3 interactions made possible the observation of perturbation-allowed transitions with selection rule k=±4, l=±3⇔k=±3, l=∓1. Furthermore, the rotational transitions J=2–1, 3–2 and 4–3 have been measured. To make use of the multiple fitting concept, the theory of reduction developed for the v_t=2 vibrational state by Sarka and Harder [K. Sarka, H. Harder, J. Mol. Spectrosc. 197 (1999) 254] has been extended to the v_t=3 vibrational state including terms up to H₆₂. Owing to problems in the reproduction of data with low K and A₁–A₂ symmetry, two types of fits have been performed using five reduced forms of the effective Hamiltonian. The first type of fit used a reduced data set for which part of the transitions has been omitted. The unitary equivalence of the determined parameter sets has been demonstrated including newly derived relations for parameters in v₁₀=3. In the second type of fit, the complete data set has been included, yielding satisfactory results only in one reduction. In both type of fits, parameters up to sixth order have been determined including the axial rotational constant A and the Coriolis constant Aζ for both values of l. General features of the direct l-type resonance spectrum in a v_t=3 level are discussed.