Microwave spectrum of DNO

The microwave spectrum of deuterated nitroxyl DNO has been observed and analyzed. The molecule was produced by the reaction of D with NO in a flow system. Both a-type and b-type transitions have been observed and the resulting rotational constants, A = 315450.3 ± 4.8 MHz, B = 38731.5 ± 1.5 MHz, and C = 34354.0 ± 1.5 MHz, are in good agreement with those of the lower electronic state ¹A′ for the electronic transition of DNO observed by Dalby. The quadrupole coupling constants for nitrogen are χ_aa = 1.03 ± 0.40 MHz, χ_bb = −6.13 ± 0.26 MHz, χ_cc = 5.10 ± 0.26 MHz. The components of the electric dipole moment of DNO have been determined to be μ_a = 1.18 ± 0.04 D and μ_b = 1.22 ± 0.04 D, giving a total dipole moment μ_total = 1.70 ± 0.05 D. The half lifetime of the molecule varies from 1 to 40 sec, depending on the condition of the surfaces of the absorption cell, which is much longer than the values reported previously.     

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.     

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,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.     

Microwave spectrum,conformation, and quadrupole coupling constants of 1-iodopropane

The molecular rotational spectrum of 1-iodopropane (n-propyl iodide) has been investigated in the frequency region 9–33 GHz. The 1-iodopropane molecule has been confirmed to exist in two rotational isomers, trans and gauche. The rotational constants of the ground state were determined to be A = 10 595.450(60) MHz, B = 1781.669(8) MHz, and C = 1614.200(7) MHz for gauche, and B = 1305.247(8) MHz and C = 1269.365(7) MHz for trans. The nuclear quadrupole coupling constants were determined to be χ_aa = −1020(3) MHz, χ_bb = 193(2) MHz, χ_cc = 827(4) MHz, χ_ab = 1173(2) MHz, χ_ac = −369(7) MHz, and χ_bc = 230(5) MHz for gauche, and χ_aa = −1509(8) MHz, χ_bb = 610(9) MHz, χ_cc = 899(12) MHz, and χ_ab = −789(9) MHz for trans. The centrifugal distortion constants were also determined using all of the assigned transitions. From the relative intensity measurements the skeletal torsional frequencies for the gauche and trans forms were estimated to be 117 and 108 cm⁻¹, respectively.     

Microwave spectrum,molecular structure,and nuclear quadrupole coupling constants of 3-bromopropene

The microwave spectra of the two ⁷⁹Br and ⁸¹Br isotopic species of 3-bromopropene were measured in the frequency region 14–23 GHz. The R and Q branches for a- and b-type rotational transitions of one conformer, skew, have been assigned and the rotational constants of the ground state have been determined to be A = 19 247.56 MHz, B = 1975.339 MHz, and C = 1914.761 MHz for ⁷⁹Br species, and A = 19 234.26 MHz, B = 1961.417 MHz, and C = 1901.563 MHz for ⁸¹Br species, respectively. By the analysis of the second-order perturbation treatment of the quadrupole interaction, it is found that the χ_ab element of the χ tensor primarily contributes to the anomalous hyperfine splittings. The matrix elements of products of direction cosines in terms of the symmetric top wavefunctions have been derived. The nuclear quadrupole coupling constants have been determined χ_aa = 384.2 MHz, χ_bb = ?71.9 MHz, χ_cc = ?276.3 MHz, and |χ_ab| = 358.7 MHz for ⁷⁹Br species and χ_aa = 283.2 MHz, χ_bb = ?55.6 MHz, χ_cc = ?227.6 MHz, and |χ_ab| = 296.0 MHz for ⁸¹Br species.     

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.     

Microwave spectrum,quadrupole coupling constants,and barrier to internal rotation of 2-iodopropene

The microwave spectrum of 2-iodopropene has been investigated between 7.7 and 18 GHz. The measured transition frequencies of the ground and two vibrationally excited states have been analyzed using direct diagonalization of the rotational and quadrupole Hamiltonian. The following rotational and quadrupole coupling constants have been determined in a leastsquares fit for the ground state: A = 9285.153(20) MHz; B = 2337.2198(14) MHz; C = 1887.5871(14) MHz; and χ_cc = ?1820.783(33) MHz; χ_ab = 147.5(10) MHz; χ_bb = 957.018(41) MHz; and χ_cc = 863.765(40) MHz. The quadrupole coupling constants have been transformed to their principal axis system. From the splittings of some transitions of the first torsionally excited state a value of V₃ = 905(3) cm^?1 has been found for the threefold barrier hindering the internal rotation of the methyl group.     

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 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.     

The millimeter wave rotational spectrum of N-cyanomethanimine,CH2NCN

The rotational spectrum of the short-lived species N-cyanomethanimine, CH₂NCN, has been measured in the frequency range 100–250 GHz. The observed transitions allow the determination of the rotational and centrifugal distortion constants and the nitrogen quadrupole coupling constants for both nitrogen nuclei. The N-cyanomethanimine spectrum was measured directly in the products of the pyrolysis of trimethylenetetrazole. The rotational constants obtained are A = 63 372.995(11) MHz, B = 5 449.347 90(28) MHz, and C = 5 009.559 86(29) MHz; the quadrupole coupling constants are χ_aa = 2.057(39) MHz and χ_bb ? χ_cc = ?7.205(21) MHz for the imine nitrogen, and χ_aa = ?3.264(33) MHz and χ_bb ? χ_cc = ?1.630(18) MHz for the cyano-group nitrogen. The accurate constants obtained allow the calculation of the line position and hyperfine structure of any rotational transition appropriate for a radioastronomical search.     

Microwave spectrum and quadrupole coupling constant tensor of chloroiodomethane

The microwave spectrum of ³⁵Cl and ³⁷Cl species of chloroiodomethane was investigated in the frequency region of 9–35 GHz. The b-type R-branch and Q-branch transitions were assigned. The rotational constants of the ground state were determined to be A = 27 418.81 ± 0.10, B = 1621.879 ± 0.024, and C = 1545.730 ± 0.044 MHz for the ³⁵Cl species; and A = 27 261.46 ± 0.16, B = 1562.240 ± 0.047, and C = 1491.008 ± 0.092 MHz for the ³⁷Cl species. From the hyperfine splitting of the I, ³⁵Cl, and ³⁷Cl nuclei, the nuclear quadrupole coupling constants were determined to be χ_aa = −1404.5 ± 3.8, χ_bb = 383.4 ± 2.1, χ_cc = 1021.1 ± 4.3, and ∥χ_ab∥ = 1176.5 ± 3.6 MHz of iodine; χ_aa = −26.8 ± 2.3, χ_bb = −11.0 ± 1.2, and χ_cc = 37.8 ± 2.6 MHz of ³⁵Cl for the ³⁵Cl species; χ_aa = −1423.2 ± 5.5, χ_bb = 389.1 ± 2.9, χ_cc = 1034.1 ± 6.2, and ∥χ_ab∥ = 1170.2 ± 6.9 MHz of iodine; and χ_aa = −20.4 ± 3.3, χ_bb = −9.1 ± 1.8, and χ_cc = 29.5 ± 3.7 MHz of ³⁷Cl for the ³⁷Cl species, respectively. The centrifugal distortion constants were also determined using all of the assigned transitions. A brief discussion of the procedure for analyzing the quadrupole hyperfine structures of a molecule containing two quadrupolar nuclei is also provided.     

Microwave spectrum of fluoroacetyl chloride

The microwave spectrum of fluoroacetyl chloride has been studied in the 8–40 GHz region and transitions arising from one conformer have been assigned. This conformer has all the heavy atoms in a plane with the fluorine and chlorine atoms trans to one another. The rotational constants and nuclear quadrupole coupling constants for the ground vibrational state are (in MHz): H₂FCCO³⁵Cl: A = 9025.82, B = 2403.92, C = 1920.70, χ_aa = ?47.7, χ_bb = 23,7, χ_cc = 24.1; H₂FCCO³⁷Cl: A = 8994.95, B = 2342.24, C = 1879.75, χ_aa = ?38.0, χ_bb = 18.9, χ_cc = 19.1. The spectrum of the first excited torsional state has been assigned. Some lines possibly due to a second conformer have been observed but not yet assigned.     

Microwave spectrum of 2-chloropyridine

The microwave spectrum of 2-chloropyridine, C₅H₄NCl, has been studied in the frequency range from 26.5–40.0 GHz. The spectrum is characterized by strong parallel type transitions of a near-prolate asymmetric top. The assigned transitions have been used to evaluate the ground state rotational constants of the two chlorine isotopes. The rotational constants are (in MHz): A = 5872.52, B = 1637.83, C = 1280.48 for the ³⁵Cl isotopic species and A = 5872.16, B = 1591.76, C = 1252.17 for the ³⁷Cl isotopic species. The small inertial defect indicates the molecule is planar. In addition an excited vibrational state of C₅H₄N³⁵Cl has been observed and analyzed. The chlorine quadrupolar coupling constants were determined for the ground state and are: χ_aa = ?71.9 MHz for ³⁵Cl and χ_aa = ?54.9 MHz for ³⁷Cl. By assuming the pyridine ring structure the CCl bond length is found to be 1.72 Å.     

The high resolution rotational spectrum of 2-cyanoaziridine

The microwave spectrum of 2-cyanoaziridine has been measured and assigned. Only the spectrum of the cis isomer has been detected although extensive searches for transitions from the trans isomer have been made, suggesting that it is at least 11 kJ mol^?1 less stable. The following nuclear quadrupole coupling constants were obtained: χ_aa(1) = ?1.249(14), χ_bb(1) = 1.407(12), χ_aa(2) = ?3.547(6), χ_bb(2) = 1.865(8) MHz, the former pair probably referring to the amino nitrogen and the latter pair to the nitrile nitrogen. The rotational constants derived from the analysis are: A = 16877.718(32), B = 3528.931(4), C = 3373.065(4) MHz, D_N = 1.10(4) kHz.     

Microwave spectrum of gauche normal propyl bromide

The microwave spectra of the two ⁷⁹Br and ⁸¹Br isotopic species of normal propyl bromide were measured in the frequency region 10–30 GHz. The a-type R-branch and b-type Q-branch transitions of one conformer, gauche, were assigned and the rotational constants of the ground state were determined to be A = 11 034.346, B = 2277.725, and C = 2024.525 MHz for the ⁷⁹Br species, and A = 11 027.924, B = 2261.019, and C = 2011.115 MHz for the ⁸¹Br species. The nuclear quadrupole coupling constants were determined to be χ_aa = 256.9, χ_bb = ?9.5, χ_cc = ?247.4, and |χ_ab| = 380.0 MHz for ⁷⁹Br species and χ_aa = 214.1, χ_bb = ?8.1, χ_cc = ?206.0, and |χ_ab| = 311.9 MHz for ⁸¹Br species. Assuming the values of χ_bc and χ_ca to be zero, the principal values of the χ tensor have been evaluated to be χ_xx = ?279.0, χ_yy = ?247.4, χ_zz = 526.4 MHz for ⁷⁹Br species and χ_xx = ?228.1, χ_yy = ?206.0, and χ_zz = 434.1 MHz for ⁸¹Br species. From the relative intensity measurements the energy differences between the ground and first excited states, and the ground and second excited states, associated with the central CC torsion around the α and β carbon bonds were found to be 127 and 211 cm^?1, respectively.     

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.     

Quadrupole hyperfine structure of the rotational spectrum of aminoacetonitrile

From high-resolution studies of the microwave spectrum of aminoacetonitrile we have established the quadrupole coupling constants of both nitrogen atoms in the molecule. They are χ_aa = ?2.77 (0.04) MHz, χ_bb = 1.20 (0.09) MHz for the amino nitrogen, χ_aa = ?3.48 (0.03) MHz, χ_bb = 1.50 (0.06) MHz for the nitrile nitrogen. Improved values for rotational constants and centrifugal distortion constants also emerge from the present spectral analysis.     

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.     

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.