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_⊥.     

Hyperfine structure of the 625 nm band in the a 3Πu ← X 1 Σg transitions of Na2

Hyperfine structures of transitions in the a ³Π_u ← X¹Σ_g system of Na₂ have been accurately measured by Doppler-free laser excitation spectroscopy in a collimated molecular beam. The hyperfine patterns are quantitatively explained and the reduced matrix elements of the magnetic dipole hf interaction determined from a least-squares fit to the measured line positions.     

CO LMR spectrum of14N16O and its analysis with spectra of14N17O and14N18O

LMR spectra for v=1←0 transitions of¹⁴N¹⁶O in X²II_{1/2, 3/2} states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of¹⁴N¹⁶O as well as¹⁴N¹⁷O and¹⁴N¹⁸O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of¹⁴N¹⁷O and¹⁴N¹⁸O were deduced.     

Laser excited fluorescence of CH in a low pressure flame

Production of CH(X²Π) in a low pressure H/O/C₂H₂ flame has been observed by laser excited fluorescence in the 0, 0 band of the A² Δ ← X²Π system at 431 nm. Laser excitation spectra have been recorded of the P, Q, and R branches with a bandwidth of 0.03 nm and of the head of the Q branch with a bandwidth of 0.0009 nm. Values of the spin—orbit and spin—rotation coupling constants in the A²Δ state have been obtained.     

ℓ-Resonance effects in C2H2 near 13.7 μm. Part H: The two quantum hotbands

This article is the second part on ℓ-resonance effects on the rotation-vibration bands of acetylene observed in the ν₅ fundamental region. While the first part concentrated on the energy level analysis of the fundamental and the seven strongest hotbands originating in the ν₄ and ν₅ excited states for both major isotopes [Spectrochim. Acta 48A, 1203 (1992)], this article summarizes the results of the analysis of the hotbands 2ν₄ + ν₅ ← 2ν₄, ν₄ + 2ν₅ ← ν₄ + ν₅, and 3ν₅ ← 2ν₅ from which improved molecular constants for the 2ν₄ and three quantum energy levels were derived for the major isotope ¹²C₂H₂. The mixing levels within the excited vibrational states due to vibrational and rotational ℓ-resonance effects are discussed which lead to the identification of the strong “forbidden” Δℓ3 band, 2ν₄+ ν³₅←2ν^Oe₄ as a result of ℓ-resonance intensity perturbation.     

The singlet nπ* states of para-benzoquinone

The vibronic nπ* singlet spectra of p-benzoquinone-h₄ and p-benzoquinone-d₄ have been observed in a supersonic jet and some as yet unknown excited state fundamentals in the vapor phase have been assigned. The electric dipole forbidden, magnetic dipole allowed origin of the ¹B_1g ← ¹A_g transition is observed at 20045 cm^?1. The origin of the¹A_u ← ¹A_g, transition has been indirectly determined at 19991 cm^?1 from the vibronic excitation spectra. Neither shows a deuterium shift.     

Time-resolved four-level double resonance in the microwave spectrum of formaldehyde

The technique of transient double resonance has been applied to the (2₁₁ ← 2₁₂)_s-(3₁₂ ← 3₁₃)_p system in the microwave spectrum of formaldehyde. An effective broadening parameter γ*/2πp=22.96±0.3 MHz Torr^?1 was measured and theory is presented to relate this to other measured multipole relaxation rates.     

Electric and Magnetic Anisotropy in Structural Organophosphorus Chemistry

Abstract

The principles of study of the electric polarizability and magnetic susceptibility anisotropy of phosphorus derivatives have been discussed. The molar constants of birefringence in the transverse magnetic field (Cotton-frlouton constants, lo¹⁸ e.m.u.) have been determined for 2-methoxy-4-methyl-1,3,2-dioxaphosphorinane (-1.31, its 2-oxoanalogue (1.5), 2-thioanalogue (-16.3), phosphorus chloride (-112), phosphorus oxychloride (-87), and thiophosphoryl chloride (-12). The principal semiaxes of molecular magnetic susceptibility ellipsoids (10²⁹ cm³) for the three latter compounds have been found equal: PCl₃ k₁ ?9.90, k _2,3 ?11.36; POCl₃ k_l ?8.83, k _2,3 ?11.28; PSCl₃ k₁ ?13.28, k_2,3, ?13.17. The components of the magnetic susceptibility tensors of the phosphorus lone pair kL ?2.15, k_t ?2.32 and of the bonds P-0 k_L ?4.35, k_T ?2.23; P-Cl k_L ?4.17, k_T ?2.05; P→O k_L ?1.11, k_T ?0.44; P→S k_L ?4.17, k_T ?2.17 have been calculated using data on the magnetic anisotropy effects on chemical shifts in PYR spectra of dioxaphosphorinanes. The relationship between the mean values of the magnetic susceptibility and electric polarizability phosphorus derivatives has been established, k = ?0.060–1.046.10^?5 b. The magnetic anisotropies of bonds have been shown to depend on their environment, for phosphoryl on the Kabachnik constants of substituents at the phosphorus atom.     

Water-soluble heteroligand complexes of 2-methyl-4-oxo-4H-pyran-3-olatoneodymium(III) with amino acids

New water-soluble heteroligand complexes of 2-methyl-4-oxo-4H-pyran-3-olatoneodymium(III) with aliphatic amino acids (glycine, N-methylglycine, and alanine) have been prepared. Within the biological “transparency window” (700–900 nm) of their electronic absorption spectra, narrow bands of Nd³⁺ are found: ⁴F_7/2 ← ⁴I_9/2; ⁴F_5/2 ← ⁴I_9/2; ⁴F_3/2 ← ⁴I_9/2 (750, 810, and 880 nm). Such complexes can be used as markers for biological tissues visualization.     

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.     

Optical and ODMR investigation of the low lying excited states of neat α-oxalic acid dihydrate

The lowest excited singlet and triplet states of neat α-oxalic acid dihydrate have been investigated by optical, optical Zeeman, and zero-field optically detected magnetic resonance (ODMR) spectroscopy at T ? 4 K. The observed electronic transitions in absorption are assigned as ¹A_u ← ¹A_g (ν₀ = 34131 cm^?1) from its normal polarizatio These correspond to the expected lowest lying ^1,3nπ* excitations in trans-α-dicarbonyls. The ³A_u → ¹A_g phosphorescence is also observed. Monitoring the phosphorescence intensity, the fine structure splittings and principal axes' orientation and the kinetic parameters of the ³A_u s The fine structure constants are X = 2510.0, Y = ?1800.3, and Z = ?709.7 MHZ where the x axis is in-plane and parallel to the carbo The absolute signs of the constants have been established by optical Zeeman measurements. The τ_x zero-field spin state has the largest total phosphorescence rate, radiative rate, and populating rate. The τ_x activity in the 0 - 0 band is polarized mainly along the x axis. However, considerable normal polarization associated with an in-p     

Multiphoton ionization spectra of two caged amines

The multiphoton ionization spectra of quinuclidine (ABCO) and triethylenediamine (DABCO) have been measured. All of the observed resonances are two-proton transitions to low-lying localized Rydberg states. For ABCO the lowest energy transitions are assigned as ¹A₁ (3s) ← ¹A₁ (n) 4.84 eV, and ¹E (3p_xy) ← ¹A₁ (n), 5.42 eV. In the case of DABCO, orbitals localized on the nitrogens interact and are split into two new orbitals. In terms of the split orbitals the low energy resonances in DABCO are assigned as ¹E′[3p_xy(?)] ← ¹A₁ (n+_, 4.44 eV, and ¹E″ [3p_xy(+)] ← ¹A₁ (n+), 4.94 eV.     

Magnetic circular dichroism and molecular orbital studies on bicyclo[6,2,0] decapentaene

The magnetic circular dichroism (MCD) spectrum of bicyclo[6,2,0] decapentaene has revealed four skeletal π → π^* electronic transitions in the visible and ultraviolet region. The four MCD bands are assigned to the B₂ ← A₁, A₁ ← A₁. B₂ ← A₁ and A₁ ← A₁ electronic transitions in increasing order of energy.     

Microwave spectra of the ground and excited vibrational states of isotopic species of nitroethylene

Rotational spectra of nitroethylene, four deuterium and six ¹³C species have been measured and analysed in the frequency range from 8 to 26 GHz. Rotational transitions in the ground state, in progressions of excited states of the NO₂ torsional mode ν₁₈, in the in-plane skeletal bending mode ν₁₃, and in doubly excited states σ₁₃+ν₁₃+ν₁₈ν₁₈ could be assigned for nitroethylene and its deuterated species. The spectra of the ¹³C isotopic species were observed in natural abundance and their assignments have partly been checked by microwave — microwave (mw — mw) double resonance. All the spectra in each of the different vibrationally excited states were found to acceptably obey a rigid rotor pattern with centrifugal distortion, corresponding to a high barrier for the NO₂ internal rotation. Rotational constants and inertia defects all show the same qualitative dependence on the internal state. The ground state rotational constants of all isotopic species have been used to determine a refined molecular structure.     

Photon echoes in the 3P0 ← 3H4 transition of Pr3+/LaF3

Photon-echo quantum beats observed in the two-pulse and three-pulse photon echo of the ³P₀ ← ³H₄ transition in Pr³⁺/LaF₃ were used to determine the excited-state spin-hamiltonian. In addition we report on the anomalous stimulated photon echo observed in the same transition which in a magnetic field may acquire a lifetime of about 30 minutes.     

Complete experimental and theoretical proton and carbon nuclear magnetic resonance spectral assignments,molecular structure and conformational study of 1‐cyclohexylpiperazine and 1‐(4‐pyridyl)piperazine

The possible stable forms and molecular structures of 1‐cyclohexylpiperazine (1‐chpp) and 1‐(4‐pyridyl)piperazine (1‐4pypp) molecules have been studied experimentally and theoretically using nuclear magnetic resonance(NMR) spectroscopy. ¹³C, ¹⁵N cross‐polarization magic‐angle spinning NMR and liquid phase¹H, ¹³C, DEPT, COSY, HETCOR and INADEQUATE NMR spectra of 1‐chpp (C₁₀H₂₀N₂) and 1‐4pypp (C₉H₁₃N₂) have been reported. Solvent effects on nuclear magnetic shielding tensors have been investigated using CDCl₃, CD₃ OD, dimethylsulfoxide (DMSO)‐d₆, (CD₃)₂CO, D₂O and CD₂Cl₂. ¹H and ¹³C NMR chemical shifts have been calculated for the most stable two conformers, equatorial–equatorial (e–e) and axial–equatorial (a–e) forms of 1‐chpp and 1‐4pypp using B3LYP/6‐311++G(d,p)//6‐31G(d) level of theory. Results from experimental and theoretical data showed that the molecular geometry and the mole fractions of stable conformers of both molecules are solvent dependent. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibration—rotation interaction in the microwave spectrum of NaOH

The rotational transition J = 4 ← 3 of NaOH in a number of vibrational states has been studied in the 100 GHz range. The coupling between the bending and stretching vibrational modes and the contribution of higher order terms in ν₂ and l² to the energy are found stronger for NaOH than for the heavier alkali hydroxides making assignment of some of the observed lines uncertain. In spite of this difficulty careful analysis yielded larger constants for the vibration—rotation interaction. A comparison is made between properties of NaOH and the heavier alkali hydroxides.     

Resonance enhanced three-photon absorption of molecular iodine

D ← X resonance enhanced three-photon excitation spectrum of iodine was observed by a cw intracavity absorption technique. Vibrational quantum numbers of D ← X transitions are given for every major spectral feature. The corresponding one-photon enhancement from the B state is evident from the one-photon vibrational assignment. The spectroscopic constants for the D state are v₀₀ = 40 998 cm^?1 ω′₀ = 113 cm^?1 and ω′₀χ′₀ = 0.045 cm^?.     

Déplacements Chimiques du Carbone 13, Constantes de Couplage 1J(CH) et 3J(CH) dans une série de dérivés trisubstitués du benzène

¹³C chemical shifts, 1-bond and 3-bond (meta) ¹³C? H coupling constants have been determined in a series of trisubstituted benzene; the substituents are Cl, NH₂, N(C₂H₅)₂, N(iC₃H₇)₂, N(C₂H₄)₂O. Chemical shifts are only in moderate agreement with the usual additivity rules. Additivity rules relative to the above mentioned coupling constants are proposed. With few exceptions, the difference between predicted and observed values is less than 10%.     

Photolysis of ozone in the ultraviolet region. Reactions of O(1D), O2(1Δg) and O≠2

Reactions of O(¹D) and O₂(¹Δ_g) with ozone have been observed time resolved by the detection of the product O³P) and their rate constants have been determined. It is found that vibrationally excited molecular oxygen, O^≠₂, also produces O(³P) in reaction with ozone. These observations are supported by the results of quantum yield determinations of the ozone decomposition in UV-photolysis.