The microwave spectrum and dipole moment of 1-cyano-1,3-cyclopentadiene

The microwave spectrum of 1-cyano-1,3-cyclopentadiene has been assigned and the rotational constants obtained are (in megahertz): A = 8356, B = 1904.24, and C = 1565.36. The dipole moment components were measured and are (in debye) μ_a = 4.25, μ_b < 0.3, μ_total = 4.25.     

The microwave spectrum of trans 1-nitropropene

Rotational transitions of 1-nitropropene arising from the ground vibrational state and from three excited states of the nitro torsional vibration have been assigned. The values of the rotational constants in MHz are: A₀=10 650B₀=2028.56C₀1722.16A₁10 615 B₁=2028.47 C₁=1725.11 A₂10 570 B₂ 2028.31 C₂= 1727.32 A₃= 10 512 B₃2028.11 C₃=1729.37The dipole moment components are μ_a = 4.52 D, μ_b = 0.42 D and μ_total = 4.54 D. From the lack of observable internal rotation splittings the barrier to internal rotation of the methyl group is shown to be greater than 2250 cal/mole.     

Microwave spectrum of 3-butyn-1-ol

The microwave spectra of 3-butyn-1-ol, in both the normal and deuterated HCCCH₂CH₂OD, species, have been assigned and one stable form of the molecule has been found to be an intramolecularly hydrogen bonded gauche form similar to the one found for the 2-haloethanols. The rotational constants for the ground vibrational state are (in MHz) as follows. HCCCH₂CH₂OH: A = 10438.35, B = 3385.87, C = 2760.54; HCCCH₂CH₂OD: A = 9998.35, B = 3378.14, C = 2723.79. Stark effect measurements yielded dipole moment components of (in D): μ_a = 0.91, μ_b = 0.85, μ_c = 0.60, and μ_total = 1.38. Assignments have also been made for two excited torsional states.     

Microwave determination of the conformation and dipole moment of 1,3-difluoroacetone

The microwave spectra of the ground state and several low-lying vibrational modes of 1,3-difluoroacetone have been assigned and analyzed. The assigned form has a molecular conformation in which one fluorine atom lies cis and the other trans to the oxygen atom. The rotational constants of the ground state species were determined using a centrifugal distortion analysis: A = 6024.843 ± 0.006 MHz, B = 2454.414 ± 0.001 MHz, C = 1783.897 ± 0.001 MHz. The molecular dipole moment components of the ground state species lie along the a and b principal axes with μ_a = 2.38 ± 0.03 D, μ_b = 0.89 ± 0.03 D, and μ_T = 2.54 ± 0.03 D. Comparative intensity measurements with OCS microwave lines indicate that the assigned form constitutes only 20% to 30% of the total gas mixture, the remainder presumably consisting of one or more other conformers, perhaps the gauche-gauche form. The lowest vibrational frequency (82 ± 12 cm^?1) is attributed to the trans-CH₂F torsion, while the next-higher vibrational frequency (127 ± 15 cm^?1) is believed to be the cis-torsion. A low-frequency in-plane bending motion is found at 285 ± 25 cm^?1.     

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.     

The microwave spectrum,dipole moment,and molecular conformation of 2-cycloheptene-1-one

The microwave spectrum of 2-cycloheptene-1-one, an unsaturated cyclic ketone, has been studied in the regions 26.5–40 and 7.0–12.4 GHz. An analysis of the ground-state “a”-type transitions yielded the rotational constants (in MHz): A = 2997.27, B = 2049.24, C = 1399.76. The “a”-type transitions of an excited vibrational state were also assigned, giving A = 3000.51, B = 2046.65, C = 1398.88. The centrifugal distortion constants, D_J and D_JK, were needed to fit the data adequately. A study of the Stark effect yielded the dipole moment components (in debye) μ_a = 3.63 ± 0.023 and μ_c = 0.882 ± 0.040. The μ_b component could not be determined from the Stark effect data. These data are used to discuss the molecular conformation of cycloheptene-1-one.     

Microwave spectrum and rotational isomerism of 3,3-difluoropropene CHF2CHCH2

The analysis of the microwave spectrum of 3,3-difluoropropene has confirmed the existence of two rotational isomers, cis and gauche. The rotational constants in the ground vibrational state are A = 9126.08 MHz, B = 3722.120 MHz, and C = 2946.598 MHz for the cis form and A = 8901.64 MHz, B = 4192.759 MHz, and C = 3107.718 MHz for the gauche form. The dipole moment and its components along the principal axes of intertia are μ_a = 2.369 ± 0.015 D, μ_c = 0.70 ± 0.03 D, and μ_t = 2.47 ± 0.03 D for the cis form and μ_a = 1.535 ± 0.015 D, μ_b = 0.53 ± 0.04 D, μ_c = 1.36 ± 0.03 D, and μ_t = 2.12 ± 0.05 D for the gauche form. The relative intensity measurement indicates that the cis form is more stable than the gauche form by 260 ± 80 cm^?1. The energy of the first excited state with respect to the ground state was found to be 63 ± 8 cm^?1 for the cis form and 85 ± 10 cm^?1 for the gauche form. Two Fourier coefficients of the potential function restricting the torsion around the CC bond were determined to be V₁ = 266 ± 40 cm^?1 and V₃ = 508 ± 200 cm^?1, using the available data. The potential function thus obtained is compared to a prediction model which is derived assuming additivity of the potential as a function of substitution.     

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 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.     

The microwave spectra and conformations of chloromethyl oxirane: cis and gauche-2 forms

The microwave spectra of two conformations of chloromethyl oxirane ($\text{CH}{}_2\text{OC}$HCH₂³⁵Cl, epichlorohydrin) is reported. In the gauche-2 form the chlorine is situated trans to the oxygen, in the cis form the chlorine is cis to the ring. The rotational constants in megahertz are gauche-2; A = 12 739.35, B = 2066.83, C = 1881.49, and cis; A = 8378.66, B = 2840.67, C = 2510.55.     

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.     

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.     

Microwave spectroscopic study of the conformations,relative energies,and dipole moments of ethyl cyanoformate

The microwave spectrum of ethyl cyanoformate displays a-type band spectra from three nearly prolate conformers. High-resolution spectra of the two more stable species have been assigned. One form, designated extended, has rotational constants A″ = 6453.3(4) MHz, B″ = 1500.47(6) MHz, C″ = 1236.36(6) MHz, which are consistent with a syn-anti [τ₁ (OCOC) = 0°, τ₂ (COCC) = 180°] structure. The second form, labeled compact, has rotational constants A″ = 6787.8(7) MHz, B″ = 1549.38(8) MHz, C″ = 1406.80(8) MHz, which are consistent with a syn-gauche [τ₁ (OCOC) = 0°, τ₂ (COCC) ～ 90°] structure. The extended form is marginally more stable, ΔE = 55 ± 27 cm^?1. The extended conformer has dipole moment components μ_a = 4.44(7), μ_b ～ 0 D and the compact conformer has dipole moment components μ_a = 4.25(7), μ_b = 0, μ_c = 1.08(23) D. The third conformer (relative energy 600 ± 140 cm^?1) has the most intense band series even at ?63°C. the bands of this conformer are unresolvable into individual rotational transitions.     

How chaotic is a state of a quantum system?

A concept related to the entropy is studied. Let A and B be two density matrices, with eigenvalues a₁, a₂,… and b₁, b₂,…, arranged in decreasing order and repeated according to multiplicity. Then A is said to be “more mixed”, or “more chaotic”, than B, if a₁?b₁, a₁+a₂?b₁+b₂,…,a₁+…+a_m?b₁+…+b_m,…; It turns out that if A is more mixed than B, then the entropy of A is larger than the entropy of B. However, more generally, let v be an arbitrary concave function, ?0, and vanishing at 0. Then, if A is more mixed than B, trv(A)?trv(B). It is shown that also the converse is true. Furthermore, a variety of other characterizations of the relation “A is more mixed than B” is obtained, and several applications to quantum statistical mechanics are given.     

Microwave spectrum and conformation of vinyl mercaptan: The syn rotamer

Rotational spectra of vinyl mercaptan (ethenethiol) CH₂CHSH and its isotopic modification CH₂CHSD have been studied by microwave spectroscpy. The molecule has been found to exist in two rotameric forms, syn and anti, associated with different orientations of the SH bond with respect to the vinyl framework. In this paper results are reported for the more stable syn form which is shown to be planar with ground state rotational constants A = 49 815.28(6) MHz, B = 5835.716(14) MHz, C = 5222.081(11) MHz, D_J = 2.85(17) kHz, D_JK = ?33.22(2.08) kHz, and δ_J = 0.425(65) kHz. Spectra have also been observed for the first and second excited states of the SH torsional vibration and the first excited state of the CCS angle bending mode. The dipole moment of the syn rotamer is μ_a = 0.813(1), μ_b = 0.376(4), and μ_total = 0.896(3) D.     

The microwave spectrum of gauche-ethylamine

The microwave spectrum of the ground state of the normal species of gauche-ethylamine CH₃CH₂NH₂ and that of -NHD, -NDH, as well as -ND₂ isotopic species were measured and assigned. The ground state splits into four substates due to two internal large amplitude motions: inversion (s and a) and internal rotation (o and e) about the CN axis. Intersystem transitions due to tunneling as well as vibrational-rotational perturbations affect not only the absorption frequencies but also the Stark effect and NQHFS. The rotational constants for the two symmetrical inversion states (s) were fitted for the normal species as (all values in MHz) A^se = 32 423.470 ± 0.184, B^se = 8 942.086 ± 0.039, and C^se = 7 825.520 ± 0.048, and A^so = 32 378.733 ± 0.182, B^so = 8 940.906 ± 0.052, and C^so = 7 825.551 ± 0.042 with the interaction constants Q_a^s = 151.12 ± 0.52 and Q_b^s = 44.4 ± 7.0. The antisymmetrical inversion states (a) were fitted as A^ae = 32 423.347 ± 0.142, B^ae = 8 942.027 ± 0.029, and C^ae = 7 825.525 ± 0.031, and A^ao = 32 378.720 ± 0.142, B^ao = 8 940.984 ± 0.029, and C^ao = 7 825.573 ± 0.031 with the interaction constants Q_a^a = 167.10 ± 0.31, Q_b^a = 48.1 ± 5.4. The energy splitting due to intersion was determined (in MHz) as Δν_inv = 1 391.39 ± 0.19 and that due to internal rotation as Δν_tors = 1 170.58 ± 0.18. The cis barrier separating the two equivalent torsional states was calculated as 690 cm^?1, and the inversion barrier between the inversion states was calculated as 1400 cm^?1, both using the Dennison-Uhlenbeck model. A simple model explaining the inversion splittings of the monodeuterated species is proposed. Comparing the relative intensities for several temperatures the gauche form was observed to be energetically higher than the trans form by 110 ± 50 cm^?1. The dipole moment could only be fitted by taking into account the internal motions yielding (in Debye) μ_a^eff = 0.11 ± 0.01, μ_b^eff = 0.65 ± 0.01, and μ_c^eff = 1.014 ± 0.015. The quadrupole coupling constants (in MHz) were found as χ_aa = ?χ⁺ = 2.268 ± 0.043 and χ_bb ? χ_cc = χ^? = 3.120 ± 0.035.     

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.     

Dipole moment of the HO2 radical from its microwave spectrum

Stark effects are measured for the 1₀₁ ← 0₀₀, 7₁₇ ← 8₀₈, and 9₀₉ → 8₁₈ transitions of the HO₂ free radical. The unresolved Stark patterns of the b-type transitions are analyzed by the use of computer simulation. Second-order perturbation theory, including the effect of spin-doublings in the denominators, is used for the calculation of the Stark effect coefficients. The dipole moment determined is μ_a = 1.412 ± 0.033 D, μ_b = 1.541 ± 0.016 D, and μ_total = 2.090 ± 0.034 D.     

The microwave spectrum and conformations of halomethyl oxiranes: Bromomethyl oxirane

The microwave spectrum of bromomethyl oxirane

has been recorded in the range 12.5–18 and 26.5–40 GHz. Lines of the two bromine isotopic species of three rotamers, gauche-1 (Br near the O atom), gauche-2 (Br near the CH₂ of the ring) and cis have been identified. The gauche-1 lines are strongest, and the cis lines the weakest. The rotational constants (in MHz) are: gauche-1 (⁷⁹Br) A = 12 296.050, B = 1 391.677, C = 1 317.360, (⁸¹Br) A = 12 199.162, B = 1 378.321, C = 1 309.142; gauche-2 (⁷⁹Br) A = 12 278.436, B = 1 378.830, C = 1 304.852, (⁸¹Br) A = 12 189.869, B = 1 369.696, C = 1 301.584; cis (⁷⁹Br) A = 7 733.314, B = 1 808.087, C = 1 737.340, (⁸¹Br) A = 7 726.16, B = 1 801.159, C = 1 730.125.     

Microwave spectrum and selenol internal rotation of 2-propaneselenol

Microwave spectra of 2-propaneselenol and its deuterated species were measured and assigned for the gauche and trans isomers. The double minimum splittings of the gauche isomers were directly observed from b-type transitions, which were assigned with the aid of a double resonance technique. Rotational constants and torsional splitting of the gauche isomer of the parent species were determined to be A = 7802.50 ± 0.75, B = 2847.68 ± 0.04, C = 2242.03 ± 0.03, ΔA = ?2.52 ± 0.74, ΔB = 0.02 ± 0.05, ΔC = ?0.34 ± 0.03, and Δν = 368.91 ± 0.94 MHz, where ΔA, and ΔB, and ΔC are the differences of the rotational constants between the (+) and (?) states. From the torsional splittings and the energy differences of the two isomers of the parent and SeD species, Fourier coefficients of the selenol internal rotation potential function were determined to be V₂ = ?88 ± 15, V₃ = 1543 ± 29 cal/mole on the assumption of V₁ = 0. Dipole moments and their components were also obtained for the two isomers.