Microwave spectrum of gauche-isopropylphosphine

The microwave spectra of isopropylphosphine has been recorded in the region 12.4–40.0 GHz. Both a- and b-type transitions were observed and assigned. The rigid rotor rotational constants were determined to be A = 7633.34 ± 0.09, B = 4243.36 ± 0.02, and C = 3045.84 ± 0.02 MHz for (CH₃)₂CHPH₂ and A = 7226.47 ± 0.05, B = 4041.06 ± 0.02, and C = 2946.85 ± 0.02 MHz for (CH₃)₂CHPD₂. Dipole moment components of |μ_a| = 1.15 ± 0.01, |μ_b| = 0.43 ± 0.01, |μ_c| = 0.03 ± 0.02 and |μ_t| = 1.23 ± 0.01 were determined from the Stark effect. From the microwave spectra, the Stark effect and the experimental rotational constants, the assigned spectrum has been identified to result from the gauche form and this conformer is believed to be more stable than the other form which is present at room temperature.     

PAM analysis of the microwave spectra of thioacetic acid,CH3COSH and CH3COSD

The microwave spectra of two isotopic species of thioacetic acid, CH₃COSH and CH₃COSD, have been studied. Using the principal axis method (PAM), including terms through n = 6 in the perturbation series and the denominator correction, the spectra were analyzed and 45 lines for CH₃COSH and 40 lines for CH₃COSD were assigned. The parameters obtained by the least-squares analysis are A = 9913.29 ± 0.56 MHz, B = 4923.11 ± 0.23 MHz, C = 3354.60 ± 0.24 MHz, θ = 57.080 ± 0.030°, s = 6.2980 ± 0.0012, and I_α = 3.198 ± 0.020 amu$\text{A}\text{?}{}^2$ for CH₃COSH, and A = 9662.80 ± 0.78 MHz, B = 4810.74 ± 0.26 MHz, C = 3273.92 ± 0.18 MHz, θ = 55.097 ± 0.024°, s = 5.9742 ± 0.0016, and I_α = 3.171 ± 0.020 amu$\text{A}\text{?}{}^2$ for CH₃COSD. The barrier to internal rotation of the methyl group is V₃ = 222.6 ± 1.4 cal/mole for CH₃COSH and V₃ = 212.9 ± 1.4 cal/mole for CH₃COSD. The Stark effect measurements of A species transitions for CH₃COSH led to the dipole moment μ = 1.821 ± 0.013 D with the components μ_a = 0.191 ± 0.010 D and μ_b = 1.811 ± 0.013 D.     

The microwave spectrum,structure, and dipole moment of the unstable molecule phosphaethene,CH2PH

A detailed rotational analysis of the microwave spectrum between 26.5 and 40 GHz of phosphaethene, CH₂PH, has been carried out. This molecule is the simplest member of a new class of unstable molecules—the phosphaalkenes. The species can be produced by pyrolysis of (CH₃)₂PH, CH₃PH₂ and also somewhat more efficiently from Si(CH₃)₃CH₂PH₂. Full first-order centrifugal distortion analyses have been carried out for both ¹²CH₂³¹PH and ¹²CH₂³¹PD yielding: A₀ = 138 503.20(21), B₀ = 16 418.105(26), and C₀ = 14 649.084(28) MHz for ¹²CH₂³¹PH. The 1₀₁-0₀₀μ_A lines have also been detected for ¹³CH₂PH, cis-CDHPH and trans-CHDPH. These data have enabled an accurate structure determination to be carried out which indicates: $\text{r(}\text{H}{}_{\mathrm{c}}\text{C}\text{) = 1.09 ± 0.015}\text{A}\text{?}\text{, ∠(}\text{H}{}_{\mathrm{c}}\text{CP}\text{) = 124.4 ± 0.8°; r(}\text{H}{}_{\mathrm{t}}\text{C}\text{) = 1.09 ± 0.015}\text{A}\text{?}\text{, ∠(}\text{H}{}_{\mathrm{t}}\text{CP}\text{) = 118.4 ± 1.2°; r(}\text{CP}\text{) = 1.673 ± 0.002}\text{A}\text{?}\text{, ∠(}\text{HCH}\text{) = 117.2 ± 1.2°; r(}\text{PH}\text{) = 1.420 ± 0.006}\text{A}\text{?}\text{, ∠(}\text{CPH}\text{) = 97.4 ± 0.4°}$. The dipole moment components have been determined as μ_A = 0.731 (2), μ_B = 0.470 (3), μ = 0.869 (3) D for CH₂PH; μ_A = 0.710 (2), μ_B = 0.509 (10), μ = 0.874 (7) D for CH₂PD.     

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.     

The microwave spectrum of C-fluorophosphaethyne FCP: Structure determination,dipole moment,and vibration-rotation data

The microwave spectrum of the new linear triatomic molecule C-fluorophosphaethyne FCP which is produced when CF₃PH₂ vapor passes over solid KOH at room temperature and ca. 20 μmHg pressure has been studied. Transitions belonging to the two isotopic variants ¹⁹F¹²C³¹P and ¹⁹F¹³C³¹P have been analyzed and the resulting structural data are $\text{r(}\text{FC}\text{) = 1.285 ± 0.005}\text{A}\text{?}$ and $\text{r(}\text{CP}\text{) = 1.541 ± 0.005}\text{A}\text{?}$. The study has yielded the following spectroscopic parameters for ¹⁹F¹²C³¹P: B₀ = 5257.80 ± 0.03 MHz, α₂ = ?11.95 ± 0.05 MHz, q₂ = 4.478 ± 0.002 MHz, and μ = 0.279 ± 0.001 Debye.     

Microwave and Raman spectra,dipole moment,barrier to internal rotation,and vibrational assignment of silylphosphine-d2

The microwave spectra of SiH₃PD₂ have been recorded in the range 26.5–40.0 GHz. Both a- and c-type transitions were observed and assigned. The rigid rotor rotational constants were determined to be A = 37589.06 ± 0.11, B = 5315.70 ± 0.02, and C = 5258.70 ± 0.02 MHz. The barrier to internal rotation has been calculated from the A-E splittings to be 1512 ± 26 cal/mole. The dipole moment components of |μ_a| = 0.22 ± 0.01, |μ_c| = 0.56 ± 0.01, and |μ_t| = 0.60 ± 0.01 D were determined from the Stark effect. By using previously determined microwave data for SiH₃PH₂, several structural parameters have been calculated and their values are compared to similar ones in other compounds. The Raman (0–2500 cm^?1) spectra of gaseous, liquid, and solid SiH₃PH₂ and gaseous SiH₃PD₂ have been recorded and interpreted in detail on the basis of C_s molecular symmetry.     

The microwave spectrum,dipole moment,and conformation of 3-oxabicyclo(3.1.0.)hexane

The microwave spectrum of 3-oxabicyclo(3.1.0.)hexane has been studied in the range 26.5–40 GHz (R-band) with a Hewlett Packard Model 8400 spectrometer. Both a and c-type R-branch transitions were used to derive the rotational constants for the ground state and first two excited states of the ring-puckering mode. The data are consistent with a single stable conformation, in agreement with a previous far-infrared study (1) and this is shown to be the boat conformation, as was the case with the similar molecules cyclopentene oxide (2, 3) (6-oxabicyclo(3.1.0.)hexane) and 3,6-dioxabicyclo(3.1.0.)hexane (1, 4). The rotational constants for the ground state are (in MHz) A = 6038.06; B = 4432.47; C = 3303.43 yielding κ = ? 0.174268. The electric dipole moment components of the ground state (in Debye units) are |μ_a| = 1.36 ± 0.02; |μ_c| = 1.03 ± 0.02 yielding a total dipole moment μ = 1.71 ± 0.03.     

The microwave spectrum of 1-phosphapropyne,CH3CP: Molecular structure,dipole moment,and vibration-rotation analysis

The J = 4 ← 3 and J = 3 ← 2 rotational transitions of 1-phosphapropyne, CH₃CP, between 26.5 and 40 GHz have been studied by microwave spectroscopy. The spectrum shows the characteristic vibration-rotation satellite patterns associated with a C_3v symmetric rotor. Apart from the most abundant isotope variant, the species ¹²CD₃¹²C³¹P, ¹²CD₂H¹²C³¹P, ¹²CH₂D¹²C³¹P, ¹³CH₃¹²C³¹P, ¹²CH₃¹³C³¹P, ¹³CD₃¹²C³¹P, and ¹²CD₃¹³C³¹P have also been studied. For ¹²CH₃¹²C³¹P the rotational constants B₀ = 4991.339 ± 0.003 MHz, D_J = 0.823 ± 0.092 kHz, D_JK = 66.59 ± 0.18 kHz have been determined. From these data the following structural parameters have been derived: $\text{r}{}_{\mathrm{s}}\text{(}\text{CH}\text{) = 1.107 ± 0.001}\text{A}\text{?}$, ∠_s(HCC) = 110.30 ± 0.09°, $\text{r}{}_{\mathrm{s}}\text{(}\text{CC}\text{) = 1.465 ± 0.003}\text{A}\text{?}$, $\text{r}{}_0\text{(}\text{CP}\text{) = 1.544 ± 0.004}\text{A}\text{?}$. The dipole moment has been determined as 1.499 ± 0.001 D by analysis of the Stark effect of the J = 3 ← 2, |K| = 1 line. The vibrational satellites (v_s = 1, 2, and 3) have been studied and various vibration-rotation parameters derived.     

Microwave measurements and calculations of quadrupole coupling effects in CH3I and CD3I

The transitions J = 1 ← 0, K = 0; J = 2 ← 1, K = 0; and J = 2 ← 1, K = 1 of CH₃I and CD₃I were measured using a Stark-modulated microwave spectrometer. Iodine quadrupole coupling strengths were analyzed to determine variations with deuterium substitution on the methyl group and variations with centrifugal distortion. Quadrupole coupling strengths were described by the expression $\text{eQq}{}_0\text{+ aJ(J + 1) + bK}{}^2\text{+}\text{cK}{}^4\text{J(J + 1)}$. Explicit expressions are given for a, b, and c for a symmetric top in terms of molecular parameters. For CH₃I eQq₀ = ?1934.11 ± 0.02 MHz and for CD₃I eQq₀ = ?1928.95 ± 0.04 MHz. Rotational constants obtained are B(CH₃I) = 7501.274 ± 0.002 MHz and B(CD₃I) = 6040.298 ± 0.007 MHz. The observed fractional change in halogen quadrupole coupling of 0.0027 is related to previous results for methyl chloride and methyl bromide.     

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.     

Rotation-inversion spectrum of methylaminoethane

Microwave spectral assignments have been made for the ground and several excited vibrational states of the normal and amino d₁ species of methylaminoethane. The inversion-rotation spectrum is consistent with a trans rotameric form with an amino inversion barrier of ～5.2 kcal mole^?1. The dipole moment of 8.88 ± 0.02 Debye has components |μ_a| = 0.00 ± 0.03, |μ_b| = 0.25 ± 0.03, and $\text{|〈 ± μ}{}_{\mathrm{c}}\text{? 〉| = 0.84 ± 0.01}$ Debye. The normal species N¹⁴ nuclear quadrupole coupling constants are (in MHz) 2.82 ± 0.09, 0.88 ± 0.13, and ?3.70 ± 0.09 for χ_aa, χ_bb, and χ_cc, respectively.     

Measurements of rotational transitions and hyperfine structure in PH2D

New rotational transition frequencies and measurements of hyperfine structure on two transitions are reported for PH₂D. All observed transitions are Q branch (ΔJ = 0) so only two independent rotational constants are obtained. These are A-C = 46 593.44 ± 0.67 MHz and κ(A-C) = 2B-A-C = ?34 545.9 ± 1.3 MHz. Nine transitions were fit to these parameters and the distortion parameter D_JK to obtain D_JK = 4.30 ± 0.04 MHz. Hyperfine structure due to spin-rotation interactions was observed on the 1₁₀ ← 1₁₁ transition at 6 024.645 MHz and on the 4₁₄ ← 4₀₄ transition at 20 815.334 MHz. Spin-rotation tensor components obtained are $\text{(M}{}_{\mathrm{aa}}\text{+ M}{}_{\mathrm{bb}}\text{)}\text{2}\text{=}\text{(M}{}_{\mathrm{aa}}\text{+ M}{}_{\mathrm{cc}}\text{)}\text{2}\text{= ?98 ± 3}\text{kHz}$.     

Non-cubic Mn2+-centers in BaF2

The EPR spectra of thermally treated BaF₂: Mn samples is reported. After thermal annealing at 900 K a trigonal Mn²⁺ center with g=2.000±0.005, |D|=2725±40MHz, |A|=265±10MHz, $\text{D}\text{A}\text{>0}$, is observed. Annealing at 1200 K produces an orthorhombic Mn²⁺ center with g=2.00±0.01, |D|=2430±40MHz, |E|=570±20MHz, |A|=265±10MHz, $\text{D}\text{A}\text{<0}$. The superhyperfine (SHF) structures due to interactions with the neighbouring fluorines indicates that the trigonal manganese interacts with four fluorines, three of them equivalent. The orthorhombic Mn²⁺ shows interaction with four equivalent fluorine nuclei.     

Microwave spectral study of 2-fluorophenol: cis conformer

The microwave spectra of 2-fluorophenol and its deuterated species have been observed and analyzed in the frequency ranges 12.5–18.0 GHz (KU band) and 21.5–26.0 GHz (K band) in the ground vibrational state at room temperature. For the normal species, the radio frequency-microwave double resonance spectrum has been recorded in the frequency range 30.0–38.0 GHz. Three rotational and five quartic centrifugal distortion constants for the normal species, $\text{A}\text{?}\text{= 3337.86 ± 0.02}$, $\text{B}\text{?}\text{= 2231.92 ± 0.01}$, $\text{C}\text{?}\text{= 1337.52 ± 0.01}$, d_J = (3.5 ± 2.9) × 10^?4, d_JK = (?4.9 ± 1.5) × 10^?3, d_K = (?3.2 ± 1.0) × 10^?3, d_WJ = (?2.0 ± 1.0) × 10^?7, d_WK = (2.6 ± 0.8) × 10^?6 (in MHz), and three rotational constants for the deuterated species, $\text{A}\text{?}\text{= 3324.70 ± 0.03}$, $\text{B}\text{?}\text{= 2177.95 ± 0.03}$, $\text{C}\text{?}\text{= 1315.96 ± 0.03}$ (in MHz), have been obtained. Consideration of the r_s coordinate of the hydroxyl hydrogen atom leads to the assignment of the spectra to the cis conformer of the molecule. An r₀ structure for the cis conformer has been proposed. The nonbonded OH ? F distance is lower by about 0.3 Å than the sum of the van der Waals radii.     

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.     

Microwave spectrum of dimethyldichlorosilane

The microwave spectrum of dimethyldichlorosilane has been observed and the rotational constants and centrifugal distortion constants have been determined for ³⁵Cl₂ and ³⁵Cl³⁷Cl species. From these constants, the molecular structure is determined as $\text{r(}\text{SiCl}\text{) = 2.055 ± 0.003}\text{A}\text{?}$, $\text{r(}\text{SiC}\text{) = 1.845 ± 0.005}\text{A}\text{?}$, ∠ClSiCl = 107.2 ± 0.3°, ∠CSiC = 114.7 ± 0.3°. An analysis of the ³⁵Cl₂ quadrupole splittings leads to quadrupole coupling constants of χ_aa = ?19.6 ± 0.3 MHz, χ_bb = ?3.7 ± 1.4 MHz, χ_cc = 23.3 ± 1.4 MHz, χ_bond = ?38.0 ± 1.6 MHz, and η_bond = 0.22 ± 0.08.     

The microwave spectrum,substitution structure and dipole moment of cyanobutadiyne,HCCCCCN

Cyanobutadiyne (cyanodiacetylene), HCCCCCN, is sufficiently stable at low pressures to permit its rotational spectrum to be studied by microwave spectroscopy. The spectrum consists of a series of R-branch transitions typical of a linear molecule. The transitions with J = 9 to 14 which lie between 26.5 and 40.0 GHz have been measured for the vibrational ground state. Transitions have also been detected in natural abundance for all possible singly substituted ¹³C and ¹⁵N isotopic species. Deuteriated cyanobutadiyne, DCCCCCN, has also been synthesized and its ground state spectrum recorded. These measurements have enabled a complete substitution structure to be derived for the first time for a polyacetylene: r₈(HC_a) = 1.0569 ± 0.001, r₈(C_aC_b) = 1.2087 ± 0.001, r₈(C_bC_c) = 1.3623 ± 0.003, r₈(C_cC_d) = 1.2223 ± 0.004, r₈(C_dC_e) = 1.3636 ± 0.003, $\text{r}{}_8\text{(}\text{C}{}_{\mathrm{e}}\text{}\text{N}\text{) = 1.1606 ± 0.001}\text{A}\text{?}\text{(10}{}^{\mathrm{?10}}\text{m}\text{)}$. The spectroscopic parameters for the ground state are B₀ = 1331.3313 ± 0.001 MHz and D₀ = 0.0257 ± 0.002 KHz. The dipole moment, determined from the Stark effects of the J = 9 and 10 lines, is 4.33 ± 0.03 Debye.     

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,dipole moment,and conformation of 3-methylcyclopentanone

The rotational spectrum of 3-methylcyclopentanone has been observed in the frequency region from 18.0 to 26.5 GHz. Both a-type and b-type transitions in the ground vibrational state and a-type transitions in five excited states have been assigned. The ground state rotational constants are determined to be A = 5423.32 ± 0.18, B = 1949.51 ± 0.01, and C = 1529.59 ± 0.01 MHz. Analysis of the measured quadratic Stark effects gives the dipole moment components ∥μ_a∥ = 2.97 ± 0.02, ∥μ_b∥ = 1.00 ± 0.03, ∥μ_c∥ = 0.18 ± 0.06, and the total dipole moment ∥μ_t∥ = 3.14 ± 0.03 D. These data are consistent with a twisted-ring conformation with a methyl group in the equatorial position.     

The microwave spectra,conformations, and dipole moments of 4-cyanocyclopentene

Microwave spectra have been observed and assigned for the axial and equatorial conformations of 4-cyanocyclopentene. For the axial species the rotational constants in megahertz are A = 5095.77, B = 2185.81, and C = 1936.50; for the equatorial species the values are A = 6762.66, B = 1916.72, and C = 1590.60. Dipole moment measurements yielded |μ_a| = 3.48 D and |μ_c| = 2.51 D for the axial form and |μ_a| = 3.85 D and |μ_c| = 1.10 D for the equatorial form. Relative intensity measurements showed the equatorial conformer to be 400 ± 60 cal mole^?1 lower in energy. Several sets of vibrational satellites were observed and natural abundance C¹³ spectra were obtained for the equatorial conformer.