Microwave spectrum of 3-lodopropene in its torsionally excited states

The microwave spectra of the skew-3-iodopropene in its torsionally excited state were studied in the region 15 to 23 GHz. From the analyses of the a-type R-branch and b-type Q-branch transitions, the rotational constants and the elements of the χ-tensor were obtained: A₁ = 17 783.84 ± 0.77, B₁ = 1591.26 ± 0.02, C₁ = 1540.24 ± 0.02, χ_aa = ?1333 ± 8, χ_bb = 386 ± 4, χ_cc = 947 ± 6, and |χ_ab| = 1086 ± 2, each in MHz for the first torsionally excited state, and A₂ = 17 915.85 ± 1.38, B₂ = 1594.49 ± 0.03, C₂ = 1541.85 ± 0.03, χ_aa = ?1319 ± 10, χ_bb = 383 ± 5, χ_cc = 936 ± 8, and |χ_ab| = 1073 ± 3, each in MHz for the second torsionally excited state, respectively. From the observed line intensity, the torsional frequencies of the CH₂I group between the ground and the first excited states and also between the first and second excited states were obtained to be 114 ± 34 and 80 ± 24 cm^?1, respectively.     

Microwave spectrum,centrifugal distortion constants,and quadrupole coupling constants of 3-chloropyridine

The microwave spectrum of 3-chloropyridine has been measured in the frequency region of 8.2 to 18 GHz. The rotational constants, centrifugal distortion constants, and the quadrupole coupling constants for the ³⁵Cl species are A = 5839.448 ± 0.027 MHz, B = 1604.152 ± 0.005 MHz, C = 1258.327 ± 0.004 MHz, Δ_J = 0.10 ± 0.01 KHz, Δ_JK = 0.36 ± 0.09 KHz, Δ_K = 1.18 ± 0.07 KHz, δ_J = ?0.008 ± 0.005 KHz, δ_K = 0.88 ± 0.20 KHz, χ_aa = ?70.04 ± 0.38 MHz, χ_bb = 36.68 ± 0.19 MHz. The values of rotational constants and quadrupole coupling constants for the ³⁷Cl species are A = 5840.052 ± 0.034 MHz, B = 1559.354 ± 0.01 MHz, C = 1230.739 ± 0.016 MHz, χ_aa = ?54.20 ± 1.26 MHz, χ_bb = 29.49 ± 0.48 MHz. The double bond character in the CCl bond is found to be 2%. The smaller than expected value of rotational constant A points to a “fattening” of the pyridine ring about the a-axis in contrast to 2-chloropyridine, where no such substitution effect was observed.     

The microwave spectrum,structure, and quadrupole coupling constants of boron chloride difluoride,BCIF2

The microwave spectrum of boron chloride difluoride, BClF₂, has been investigated in the region 26.5–40.0 GHz. R-branch transitions belonging to the isotopic species ¹¹B³⁵Cl¹⁹F₂, ¹¹B³⁷Cl¹⁹F₂, and ¹⁰B³⁵Cl¹⁹F₂ have been observed and the derived rotational constants yield the following ground-state structural parameters: $\text{r}{}^0\text{(BF) = 1.315 ± 0.006}\text{A}\text{?}$, $\text{r}{}^{\mathrm{s}}\text{(BCl) = 1.728 ± 0.009}\text{A}\text{?}$, < FBF = 118.1 ± 0.5°. The ground-state rotational constants of the most abundant species ¹¹B³⁵Cl¹⁹F₂ are: A₀ = 10 449.32 ± 0.13, B₀ = 4705.811 ± 0.020, C₀ = 3239.702 ± 0.026 MHz, Δ_JK = 8.9 ± 1.7, and Δ_J = 1.86 ± 0.48 KHz. The asymmetry parameter κ = ?0.593291 and the inertial defect δ⁰ = 0.2361 amu Ų which is consistent with that expected for this type of molecule if planar. The ³⁵Cl quadrupole coupling constants for ¹¹B³⁵Cl¹⁹F₂ are χ_aa = ?42.8 ± 1.0, χ_bb = 30.2 ± 1.5, χ_cc = 12.6 ± 1.5 MHz with the asymmetry parameter η = 0.41.     

Electronic structure of arsabenzene: Microwave spectrum,dipole moment,and nuclear quadrupole coupling constants

The microwave spectrum of arsabenzene was analyzed; a dipole transitions were observed. The following rotational constants were obtained; A = 4871.03 ± 0.18 MHz, B = 2295.87 ± 0.01 MHz, C = 1560.10 ± 0.01 MHz. The dipole moment was 1.10 ± 0.04 D. The nuclear quadrupole coupling constants due to the ⁷⁵As nucleus were χ_aa = ?186.4 ± 0.1 MHz, χ_bb = 43.5 ± 0.2 MHz, χ_cc = 142.9 ± 0.2 MHz, and the asymmetry parameter, η = 0.533 ± 0.002. Analysis of the quadrupole coupling constants indicated that the population of the 4p orbitals on arsenic decrease in the order n_a > n_b > n_c.     

Microwave spectrum,barrier to internal methyl rotation,dipole moment,and partial structure of dimethylketene

From the microwave spectrum of dimethylketene which has been recorded from 8 to 37 GHz, the following rotational constants were derived: A = 8 267.832 ± 0.8, B = 3 884.101 ± 0.03, C = 2 728.826 + 0.03 MHz. The dipole moment is μ_a = 1.94 ± 0.01 D. Substitution coordinates for all methyl group atoms have been obtained by investigating the spectra of six isotopic species of the molecule. The potential barrier V₃ hindering internal rotation of the methyl tops has been fitted to the multiplet width of a number of high-J ground state ^aQ-transitions which were observed as triplets. V₃ is 2065 cal/mole, keeping fixed I_α = 3.132 amu Ų and angle (methyl-top to a-axis) = 58.94° as obtained from the partial substitution studies.     

The microwave spectrum of trans-ethylamine

The microwave spectrum of normal trans-ethylamine CH₃CH₂NH₂ and that of the -NHD and -ND₂ species were measured and assigned. The obtained rotational constants for the ground state of the normal species are (in MHz): A = 31 758.33 ± 0.08, B = 8749.157 ± 0.025, and C = 7798.905 ± 0.025. The fitted dipole moment components are (in Debye): |μ|_a = 1.057 ± 0.006, |μ_b| = 0.764 ± 0.009, and |μ_t| = 1.304 ± 0.011. The quadrupole coupling constants were fitted as (in MHz): χ⁺ = 1.62 ± 0.035 and χ^? = ?1.89 ± 0.08. Analysis of the HFS of the deuterated species -ND₂ allowed the experimental determination of the principal quadrupole tensor values (in MHz): χ_zz = ?4.68 ± 0.20, χ_yy = 1.75 ± 0.06, and χ_xx = 2.93 ± 0.20. The angle between the CN bond and the direction of the χ_zz quadrupole tensor component was fitted as 108.9° ± 0.6° and agreed with the expected general direction of the lone electron pair.     

13C−1H heteronuclear dipolar correlation studies of the hydrogen bonding of the quinones inRhodobacter sphaeroides R26 reaction centers

The photosynthetic reaction center (RC) of the photosynthetic bacteriumRhodobacter sphaeroides R26 contains two quinones, Q_A and Q_B. Solid-state heteronuclear (¹H?¹³C) dipolar correlation spectroscopy has been used to study the binding of the quinones in the ground state for RCs reconstituted with l-¹³C ubiquinone-10. Lee-Goldburg cross-polarization buildup curves are recorded to determine distancesr _CH between the l-¹³C carbon labels and the protons involved in the polarization transfer. The l-¹³C of both Q_A and Q_B have intermolecular correlations with protons that resonate downfield, in the region of hydrogen-bonding protons. The distances between the carbon labels and the correlated protons are short, 0.21±0.01 nm. Hence the nuclear magnetic resonance provides evidence for strong hydrogen-bonding interactions at the l-C=O of both Q_A and Q_B for RCs in the ground state. The environment of the l-¹³C of the Q_B is structurally heterogeneous compared to that of the Q_A. The data can be reconciled with a strong H-bonding interaction of the l-C=O of Q_A with Ala M260 NH, and with complex hydrogen bonding involving NH of Ile-L224 and of Gly-L225, and possibly the Ser-L223 hydroxyl group of the l-C=O of the Q_B, in the proximal site.     

Dynamics of [n.3]paracyclophanes (n = 2 – 4) as studied by NMR. Obtaining separate Arrhenius parameters for two dynamic processes in [4.3]paracyclophane

Extending our earlier findings for [3.3]paracyclophane, NMR line shape studies of the conformational dynamics in [3.2] and [4.3]paracyclophanes are reported, of which the former is conformationally homogeneous and the latter occurs in two enantiomeric forms. For [3.2]paracyclophane, the Arrhenius activation energy E_a = 11.6 ± 0.1 kcal/mol and preexponential factor log (A/s^?1) = 12.92 ± 0.07 were found. In [4.3]paracyclophane, the conformational dynamics are quite complicated because, apart from interconversions of each enantiomer into itself proceeding via inversion of the propano bridge with rate constant k₁, the enantiomers mutually rearrange with rate constant k₂ due to inversion of the butano bridge. The determination of Arrhenius parameters from dynamic ¹H spectra of the aromatic protons for these two conformational processes (E_a = 11.2 ± 0.5 kcal/mol and log (A/s^?1) = 13.6 ± 0.5 for the former, and E_a = 9.7 ± 0.4 kcal/mol and log (A/s^?1) = 13.2 ± 0.4 for the latter) is the highlight of this work. In the investigated temperature range, in [4.3]paracyclophane, the occurrence of other conformational processes beyond those mentioned above can be excluded, because they would produce different line shape patterns than those actually observed. Copyright © 2013 John Wiley & Sons, Ltd.     

Momentum distribution of charged particles in jets in dijet events and comparison to perturbative QCD predictions

Inclusive momentum distributions of charged particles are measured in dijet events. Events were produced at the AMY detector with a centre of mass energy of 60 GeV. Our results were compared, on the one hand to those obtained from other e⁺e^?, ep as well as CDF data, and on the other hand to the perturbative QCD calculations carried out in the framework of the modified leading log approximation (MLLA) and assuming local parton–hadron duality (LPHD). A fit of the shape of the distributions yields Q_eff = 263±13 MeV for the AMY data. In addition, a fit to the evolution of the peak position with dijet mass using all data from different experiments gives Q_eff = 226±18 MeV. Next, α_s was extracted using the shape of the distribution at the Z⁰ scale, with a value of 0.118 ± 0.013. This is consistent, within the statistical errors, with many accurate measurements. We conclude that it is the success of LPHD + MLLA that the extracted value of α_s is correct. Possible explanations for all these features will be presented in this paper.     

Microwave spectrum,structure, dipole moment,quadrupole coupling constant,and internal motion of thioformamide

The r_s structure of thioformamide has been determined from the microwave spectra of the normal as well as isotopic species of the molecule. The structural parameters obtained assuming the planarity of the molecule are $\text{NH}{}_{\mathrm{c}}\text{= 1.001}{}_8\text{± 0.006}\text{A}\text{?}\text{,}\text{NH}{}_{\mathrm{t}}\text{= 1.006}{}_5\text{± 0.003}\text{A}\text{?}\text{,}\text{CN}\text{= 1.358}{}_2\text{± 0.003}\text{A}\text{?}\text{,}\text{CS}\text{= 1.626}{}_2\text{± 0.002}\text{A}\text{?}\text{,}\text{CH}{}_{\mathrm{a}}\text{= 1.09}{}_6\text{± 0.08}\text{A}\text{?}\text{, ?}\text{H}{}_{\mathrm{c}}\text{NH}{}_{\mathrm{t}}\text{, = 121°42′ ± 40′, ?}\text{H}{}_{\mathrm{c}}\text{NC}\text{= 117°55′ ± 40′, ?}\text{H}{}_{\mathrm{t}}\text{NC}\text{= 120°22′ ± 30′, ?}\text{NCS}\text{= 125°16′ ± 15′ ?}\text{NCH}{}_{\mathrm{a}}\text{= 108°}{}_{\mathrm{5\prime }}\text{± 5°,}\text{and}\text{?}\text{SCH}{}_{\mathrm{a}}\text{= 126°}{}_{\mathrm{39\prime }}\text{± 5°}$.The dipole moment is calculated from the Stark effects of the three transitions to be μ_a = 3.99 ± 0.02 D, μ_b = 0.13 ± 0.25 D, and μ_total = 4.01 ± 0.03 D, where the c component is assumed to be zero.The quadrupole coupling constant of the ¹⁴N nucleus is estimated using the doublet splittings observed for six Q-branch transitions; χ_cc - χ_bb = ?5.39 ± 0.15 MHz and χ_aa = 2.9 ± 1.2 MHz.Two sets of vibrational satellites are observed and assigned to the first excited state of the amino wagging and the NCS bending vibrations, respectively. The relative intensity measurement gives the vibrational energies of 393±40 cm^?1 and 457 ± 50 cm^?1 for NH₂CHS and 293 ± 30 cm^?1 and 393 ± 40 cm^?1 for ND₂CHS. The amino wagging inversion vibration in the molecule is discussed in comparison with that in formamide. It is most probable that the thioformamide molecule is also planar without any potential hump to the amino inversion at the planar configuration.     

The microwave spectrum of 4-pyridine carbaldehyde (isonicotinealdehyde)

The microwave spectrum of 4-pyridine carbaldehyde has been investigated in the region 8 to 40 GHz. Rotational transitions have been observed and assigned for the ground state and two excited states of the torsion mode. Analysis yields precise rotational constants (A = 5519.04 ± 0.08, B = 1559.17 ± 0.03, C = 1216.11 ± 0.02 MHz) which prove the molecule to be planar. Centrifugal distortion constants have also been obtained. Analysis of the observed ¹⁴N quadrupole fine structure yields the following quadrupole coupling constants (in MHz): χ_aa = ?4.67 ± 0.09; χ_bb = 1.19 ± 0.26; χ_cc = 3.48 ± 0.26. The electric field gradient about the nitrogen nucleus is thus similar to that of pyridine.     

Microwave spectrum,conformation, quadrupole coupling constants,and barrier to internal rotation of methoxyamine

The microwave spectra of three isotopic species of methoxyamine (CH₃ONH₂) have been studied. For the normal species the ground-state rotational constants are A = 42488 ± 150 MHz, B = 10049.59 ± 0.03 MHz, and C = 8962.85 ± 0.03 MHz. From these data and those from the -NHD and -ND₂ species, the amino protons have been shown to occupy a symmetrical trans position relative to the methyl group. The barrier to internal rotation of the methyl group has been found to be 873 ± 15 cm^?1 by analysis of ground-state splittings. Analysis of hyperfine splittings has yielded the ¹⁴N quadrupole coupling constants, which have the following values for the normal isotopic species: χ_aa = 3.63 ± 0.03 MHz, χ_bb = ?3.69 ± 0.07 MHz, and χ_cc = 0.06 ± 0.07 MHz.     

The microwave spectrum,structure and nuclear quadrupole coupling constants for stibabenzene

The microwave spectrum of 121-SbC₅H₅, 123-SbC₅H₅, β-dideutero 121-SbC₅H₃D₂ and 123-SbC₅H₃D₂ has been assigned in the region 26.5–40.0 GHz. The respective rotational constants and uncertainties are: A = 4512.69 ± 0.42, B = 1738.00 ± 0.01, C = 1254.51 ± 0.01; A = 4512.84 ± 0.30, B = 1729.80 ± 0.01, C = 1250.22 ± 0.01; A = 4176.18 ± 0.33, B = 1660.94 ± 0.01, C = 1188.15 ± 0.01; A = 4176.60 ± 0.61, B = 1652.94 ± 0.03, C = 1184.03 ± 0.03 (in MHz units). The structure is found to be planar, C_2v in symmetry. The $\text{d(}\text{Sb-C}\text{) = 2.050 ± 0.005}\text{A}\text{?}$ and ∠CSbC = 92.9° ± 1.0°. The nuclear quadrupole coupling constants for the 121 and 123 antimony isotopes are χ_aa = 456.4 ± 4.1 MHz, η = 0.396 ± 0.008, and χ_aa = 583.00 ± 5.3 MHz, η = 0.399 ± 0.008, respectively. Several alternate techniques using the coupling constants as data support a σ-donating property for antimony.     

Microwave spectrum and substitution structure of methylene chloride

The microwave spectrum of methylene chloride has been reinvestigated in order to obtain a complete substitution (r_s) structure of well-defined precision. Measurements on the ¹³CH₂Cl₂ species have yielded the following rigid-rotor rotational constants: A = 30746.20 ± 0.10 MHz, B = 3320.63 ± 0.11 MHz, and C = 3053.44 ± 0.10 MHz. These data, combined with revised values reported earlier for other isotopic species, yields the following r_s structural parameters: CCl = 1.767 ± 0.002 Å, CH = 1.085 ± 0.002 Å, ∠HCH = 112.1 ± 0.2°, and ∠ClCCl = 112.2 ± 0.1°.     

Hyperfine-structure measurements on Dy161 and Dy163

In an atomic beam magnetic resonance experiment the hyperfine interaction constantsA andB of the⁵ I ₈ groundstate of Dy¹⁶¹ and Dy¹⁶³ were found to be Dy¹⁶¹:A=?(115.8±1)MHz, Dy¹⁶³:A=(162.9±0.6)MHz,B=(1102±15)MHz,B=(1150±20)MHz. Using an effective value for 〈r^?3〉, the magnetic moments and electric quadrupole moments of the Dy¹⁶¹ and Dy¹⁶³ nuclei were calculated to be Dy¹⁶¹:μ _I=?(0.47±0.09) n.m., Dy¹⁶³:μ _I=(0.66±0.13)n.m.,Q=(2.36±0.4)barns,Q=(2.46±0.4)barns.     

Microwave spectrum,conformation, and quadrupole coupling constants of cyclopentyl chloride

The microwave spectra of the normal and two isotopic species of cyclopentyl chloride have been observed and analyzed. For the normal isotopic species the rotational constants (in MHz) are A = 4547.77 ± 0.01, B = 2290.22 ± 0.01, and C = 2073.34 ± 0.01. From the rotational constant data, it has been shown that the stable molecular conformation is the bent axial form. Quadrupole coupling constants have been measured for the ³⁵Cl nucleus, the values being (in MHz) χ_aa = ?23.70 ± 0.10, χ_bb = 32.33 ± 0.36, and χ_cc = ?8.63 ± 0.37. When transformed to the CCl bond axis system, the coupling constants confirm the axial structure. Extensive vibrational satellite structure, presumably arising from the pseudorotational ring mode with a fundamental frequency of 52 ± 5 cm^?1, has been observed and assigned. No spectral evidence has been observed for a second stable molecular conformer.     

Microwave spectral studies of rotational isomerism in substituted ethanethiols: 2-Aminoethanethiol and 2-chloroethanethiol

Microwave spectra were observed and analyzed for 2-aminoethanethiol and 2-chloroethanethiol. The amino compound exists in two gauche rotameric conformations, one exhibiting an intramolecular SH?N hydrogen bond. The hydrogen-bonded conformer lies higher in energy by 274 ± 90 cal mole^?1 and has the following rotational constants (in MHz): A = 12 040.1 ± 11.3, B = 3352.24 ± 0.03, and C = 2881.99 ± 0.03. For the non-hydrogen-bonded conformer the rotational constants (in MHz) are A = 11 929.9 ± 10.2, B = 3395.01 ± 0.03, and C = 2877.82 ± 0.03. Dipole moment measurements for the H-bond conformer led to μ_a = 2.68 D, μ_b = 0.88 D, and μ_c = 0.37 D, while for the non-H-bond form the values are μ_a = 1.51 D, μ_b = 0.0 D, and μ_c = 0.62 D. In the case of chloroethanethiol, the only assigned spectral lines were the unresolved J → J + 1 a-type bands of a trans conformation. For this molecule the combination rotational constant B + C has the value 2955.17 ± 0.02 MHz for the ³⁵Cl species and 2879.73 ± 0.02 MHz for the ³⁷Cl species.     

Internal rotation in methyl silane by avoided-crossing molecular-beam spectroscopy

The avoided-crossing molecular-beam electric-resonance technique was applied to methyl silane in the ground torsional state. A new type of anticrossing is introduced which breaks the torsional symmetry and obeys the selection rules ΔJ = 0, K = +1 /a3 ?1. For these “barrier” anticrossings, the values of the crossing fields E_c yield directly the internal rotation splittings; the E_c are independent of the difference (A-B) in the rotational constants. Such anticrossings were observed for J from 1 to 6. Studies were also conducted of several “rotational” anticrossings (J, K) = (1, ±1) /a3 (2, 0) for which E_c does depend on (A-B). The normal rotational transition (J, K) = (1, 0) ← (0, 0) was observed in the ground torsional state using the molecular beam spectrometer. The present data on CH₃²⁸SiH₃ were combined with Hirota's microwave spectra and analyzed with the torsion-rotation Hamiltonian including all quartic centrifugal distortion terms. In addition to evaluating B and several distortion constants, determinations were made of the moment of inertia of the methyl top I_α = 3.165(5) amu-Ų, the effective rotational constant A^eff = 56 189.449(32) MHz, and the effective height of the threefold barrier to internal rotation V₃^eff = 592.3359(73) cm^?1. The correlations leading to these two effective constants are discussed and the true values of A and V₃ are determined within certain approximations. For the isotopic species CH₃³⁰SiH₃, barrier and rotational anticrossings were observed. The isotopic changes in A and V₃ were determined, as well as an upper limit to the corresponding change in I_α.     

Microwave spectrum of nitroxyl

The microwave spectrum of HNO has been observed and analyzed. Both a-type and b-type transitions have been measured. The rotational constants obtained are A = 553903.0 ± 2.7 MHz, B = 42308.52 ± 0.10 MHz, and C = 39169.46 ± 0.10 MHz. In the analysis of the spectrum, centrifugal distortion corrections are tentatively taken into account by using the centrifugal distortion constants determined by Dalby. The quadrupole coupling constants for nitrogen in HNO are determined to be χ_aa = 0.36 ± 0.56 MHz, χ_bb = ? 5.46 ± 0.30 MHz, and χ_cc = 5.10 ± 0.26 MHz. The dipole moment and its components determined from the Stark effect measurement are μ_total = 1.67 ± 0.03 D, μ_a = 1.03 ± 0.01 D, and μ_b = 1.31 ± 0.02 D. The microwave spectrum of DNO has been reanalyzed by taking into account the centrifugal distortion effect. The inertia defects for HNO and DNO have been calculated. The results are limited in precision by the lack of reliable force constants.     

Static quadrupole moments of the first excited states of 200Hg and 202Hg

The static quadrupole moments Q_2⁺ and B(E2; 0⁺ → 2⁺) values of the 2⁺ first excited states of ²⁰⁰Hg and ²⁰²Hg have been determined using the reorientation effect in Coulomb excitation. An annular silicon surface-barrier detector was used to detect backscattered ⁴He, ¹²C and ¹⁶O projectiles. It is found that for ²⁰⁰Hg, Q_2⁺ = +1.07 ± 0.19 e · b(+0.98 ± 0.19 e · b) for destructive (constructive) interference from the 2^+′ state, and B(E2; 0⁺ → 2⁺) = 0.853 ± 0.007 e² · b². For ²⁰²Hg, we find Q_2⁺ = +1.01 ± 0.13 e · b (+0.87 ± 0.13 e · b) and B(E2; 0⁺ → 2⁺) = 0.605 ± 0.005 e² · b². The Q_2⁺ value obtained for ²⁰⁰Hg is in agreement with previous work, but that for ²⁰²Hg is not. The results obtained are compared with the predictions of various nuclear models, and the mass dependence of Q_2⁺ in the region 182 ≦ A ≦ 206 is examined.