Pulsed-nozzle Fourier Transform Microwave Spectroscopy Research Articles

Ground-state rotational spectrum of CH 3NC⋯HCN and the nature of hydrogen bonds involving triply-bonded carbon

The ground-state rotational spectra of the hydrogen-bonded species CH 3NC⋯HCN and CH 3NC⋯DCN have been studied using the technique of pulsed-nozzle Fourier-transform microwave spectroscopy. The spectra were of the symmetric-top type and their analysis led to the rotational constants B 0 = 969.0435(4) MHz and 964.7530(5) MHz for the parent and deuterated molecule, respectively. The centrifugal distortion constants, D J and D JK , were established to be 0.369(7) kHz and 40.8(2) kHz for CH 3NC⋯HCN, and 0.356(8) kHz and 39.4(2) kHz for the deuterium species, while the corresponding 14N-nuclear coupling constants were χ( 14N) = −4.23(11) MHz and −4.5(1) MHz. Analysis of the centrifugal constants D J using a model of C 3v symmetry with the atoms arranged in the order H 3CNC⋯HCN gave the quadratic force constant associated with stretching of the hydrogen bond as 9.3(1) N m −1 and 9.7(1) N m −1 in CH 3NC⋯HCN and CH 3NC⋯DCN, respectively. The distances in these isotopomers between the carbon nuclei adjacent to the hydrogen bond r(C⋯C), were found to be 3.433(3) Å and 3.420(3) Å, when using a model that compensates for the contributions of the intermolecular bending modes to the zero-point motion.

Pulsed-nozzle Fourier-transform microwave spectroscopy of laser-vaporized metal oxides: Rotational spectra and electric dipole moments of YO, LaO, ZrO, and HfO

The rotational spectra of YO, LaO, ZrO, and HfO have been measured using a Fourier-transform microwave spectrometer in combination with a laser-ablation source. Here, a Q-switched Nd:YAG laser (532 nm) was used to vaporize the metal oxides from a target source rod located in the throat of a pulsed-molecular-beam valve. A description of the instrument is given. The electric dipole moments of the four species have been measured and compared to ab initio results, where available. The experimental values are μYO =4.524(7), μLaO =3.207(11), μZrO =2.551(11), and μHfO =3.431(5) D. Of special note are the extremely large nuclear quadrupole coupling constants, eQq, determined for the 177HfO and 179HfO isotopic species, with values of −5952.649(35) MHz and −6726.981(39) MHz, respectively. This is the first determination of nuclear quadrupole coupling constants for a molecule containing the Hf atom.

Pure rotational spectrum of the mercury–argon van der Waals complex

The pure rotational spectrum of the mercury–argon complex has been observed by pulsed-nozzle Fourier-transform microwave spectroscopy. Rotational constants, determined for six major isotopic species of mercury, fix the mercury–argon distance of 4.053 Å. The eQq constant for 201Hg⋅Ar is estimated to be less than 0.5 MHz and indicates small perturbation on the electric charge distribution of mercury when the complex is formed.

Pulsed-nozzle Fourier-transform microwave spectroscopy of C 2H 2·Ar complex

The rotational spectrum of C 2H 2·Ar has been studied by pulsed-nozzle Fourier-transform microwave spectroscopy. The complex is shown to have C 2v symmetry. The Ar atom is located 4.04 Å from the center of mass of C 2H 2; the distance between the adjacent Ar and C atoms is 0.7 Å larger than that expected from the van der Waals contact. The extremely low van der Waals bending frequency (≈9 cm -1) estimated from analysis of the centrifugal distortion constants indicates small anisotropy in the intermolecular potential of this complex.

Infrared and microwave spectra of OCO–HF and SCO–HF

The H–F stretching bands of the OCO–HF and SCO–HF complexes have been studied by optothermal (bolometer-detected) molecular-beam spectroscopy. Both species exhibit spectra of a quasilinear molecule red shifted from free HF by 52.1 and 57.5 cm−1, respectively. The principal band in both molecules is accompanied by a slightly red-shifted doublet-type subsidiary band that can be interpreted as a hot band of a low frequency bending vibration or a K=1 subband of a bent molecule. Accurate doublet splittings in the ground H–F vibrational state have been measured by pulsed-nozzle Fourier-transform microwave spectroscopy.

Electric-dipole moments of H 2O-formamide and CH 3OH-formamide

Electric-dipole moments have been determined for H 2O-formamide and CH 3OH-formamide by pulsed-nozzle Fourier-transform microwave spectroscopy. For H 2O-formamide μ a =1.050(1) D and μ b =2.135(3) D while for CH 3OH-formamide μ a =1.066(1) D and μ b =2.091(2) D. The corresponding complexation-induced moments are estimated as 0.55 D and 0.34 D for H 2O-formamide and 0.58 D and 0.10 D for CH 3OH-formamide. The results are compared with theoretical calculations.

79Br-Nuclear quadrupole coupling in the rotational spectrum of HC 15N⋯D 79Br: determination of the H(D)Br oscillation amplitudes and force constant

The ground-state rotational spectrum of the linear, hydrogen-bonded isotopomer HC 15N⋯D 79Br has been investigated by pulsednozzle Fourier-transform microwave spectroscopy to give the spectroscopic constants B o = 1374.4429(3) MHz, d j = 1.790(9) kHz, χ( 79Br) = 438.645(9) MHz and M( 79Br) = 2.4(3) kHz. The HBr subunit oscillation amplitudes /gb av H = 15.069(8)° and β AV D = 12.726 (7)°, determined by combined use of X( 79Br) for HC 15N⋯H 79Br and HC 15N⋯D 79Br, lead to the HBr oscillation force constant k ββ=6.93(2) × 10 −20J rad −2. The variation of k ββ with k ββ is considered for the series B⋯HX, where B = CO, PH 3, HCN and X = Cl or Br.

First-order stark effect and electric dipole moment of H 3P … HC 15N by pulsed-nozzle fourier-transform microwave spectroscopy

The first-order Stark effect in the J = 4 ← 3, K = 1 transition of the weakly bound dimer H 3P … HC 15 N has been obeserved and measured by pulsed-nozzle Fourier-transform microwave spectroscopy under the selection rules Δ M = O and Δ M = ± 1. The electric dipole moment μ= 4.046(47) D determined for H 3P … HC 15 N has been interpreted in terms of an enhancement Δμ = 0.60 D on dimer formation.

D-nuclear quadrupole coupling in the rotational spectrum of 15N 2…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 15N 2…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, 15N 2, CO, PH 3, H 2S, HC 15N and H 2O.