Millimeter-wave spectrum of the C4v molecule iodine oxygen pentafluoride IOF5: K-doubling of the |k| = 2 transitions in the ground state spectrum

Measurements are reported for the rotational spectrum of the C_4v molecule IOF₅ in the ground vibrational state in the range 30–75 GHz (J7 ← 6 to J17 ← 16). The K-doubling of |k| = 2 transitions due to an off-diagonal centrifugal distortion interaction of the type (Δl, Δk) = (0, ±4) has been observed. The centrifugal distortion constants D_J, D_JK, and R₆ have been determined as 0.139(2) kHz, 0.107(4) kHz, and 21(2) Hz, respectively.     

The infrared spectrum of 31P14N near 1300 cm−1

The infrared absorption spectrum of the PN molecule has been measured at temperatures between 800 and 1050°C with a tunable diode laser. The transitions measured ranged from J″ = 3 to J″ = 53 and included the vibrational transitions v = 1 ← 0, 2 ← 1, 3 ← 2, and 4 ← 3. These measurements are combined with microwave measurements made by others to yield a consistent set of ten Dunham ro-vibrational constants and their uncertainties.     

Far infrared spectrum and spectroscopic constants of AsH3 in the ground state

The far ir spectrum of arsine, AsH₃, was recorded in the range 25–100 cm^?1 with a resolution of approximately 0.004 cm^?1. ΔJ = +1, ΔK = 0 rotational transitions were measured and assigned up to J″ = 12. These transitions, together with the presently available microwave and submillimeter-wave data and ground state combination differences, were analyzed on the basis of a rotational Hamiltonian which includes Δk = ±3 and Δk = ±6 interaction terms. The derived ground state molecular parameters reproduced the transition frequencies of both allowed and “perturbation allowed” transitions within the accuracy of the measurements. The equilibrium structure was determined for the AsH₃ molecule.     

Methyl isocyanate: An analysis of the low-J rotational spectrum using the quasi-symmetric top molecule approach

The low-J rotational spectrum of methyl isocyanate (CH₃NCO) has been analyzed in terms of the quasi-symmetric top molecule model, accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. An assignment of 25 J = 1 ← 0 and 2 ← 1 rotational transitions arising from the various CNC bending and torsional states is proposed. The molecule is found to be a nearly freely internally rotating quasi-symmetric top, with a barrier to linearity of the CNCO skeleton of 1049 cm^?1 and an equilibrium CNC valence angle of 140.2°.     

M-dependence of collisional transfer of rotational energy in OCS mixtures

Collision-induced transitions between rotational levels of OCS in the ground vibrational state have been investigated by steady-state microwave double resonance, with the M sublevels separated by a Stark field. The (2 ← 1)_P-(1 ← 0)_S, (3 ← 2)_P-(1 ← 0)_S, and (4 ← 3)_P-(1 ← 0)_S systems have been studied for pure OCS and for mixtures with excess CH₃OH, He, and H₂. For four-level systems having dipolar connections (ΔJ = 1; ΔM = 0, ± 1; parity ± ? ?) between pump and signal levels, it is found for OCS and the OCS-CH₃OH mixture that the dipole-type ΔJ = 1 transitions always dominate the collisional transfer, but for the OCS-He and OCS-H₂ mixtures that ΔJ = 2 quadrupole-type transitions are dominant. For all four collision partners, significant ΔJ = 2 and ΔJ = 3 collisional transfer is observed in some systems, indicating the presence of high-order terms in the collisional interaction.     

Infrared-microwave double resonance in CH3OH using a Zeeman-tuned 3.5-μm HeXe laser

Infrared microwave double resonance signals have been observed for CH₃OH using the 3.5-μm HeXe laser line. When microwave transitions in the ground vibrational state are pumped, the double resonance signals are obtained on two infrared transitions v = 1 ← 0 of ν^CH(a′); v = 1, J, K, μ = 4, 2, 1 ← v = 0, J, K, μ = 3, 2, 1, and 4, 3, 1 ← 3, 3, 1. Three weak double resonance signals are due to the collision-induced transitions. Their relative intensities have been explained successfully by using the rate constants of collision-induced transitions which are proportional to the dipole matrix elements between the states involved in the transitions.     

Doppler-limited dye laser excitation spectroscopy of HCF

The cw dye laser excitation spectrum of the $\text{A}\text{?}{}^1\text{A″(000) ←}\text{X}\text{?}{}^1\text{A′(000)}$ vibronic band of HCF was observed between 17 188 and 17 391 cm^?1 with the Doppler-limited resolution, 0.04 cm^?1. The HCF molecule was produced by the reaction of discharged CF₄ with CH₃F, and 853 lines were observed, of which 516 transitions were assigned to K′_a ← K″_a = 3 ← 4, 2 ← 3, 1 ← 2, 0 ← 1, 1 ← 0, 2 ← 1, 0 ← 0, 1 ← 1, 2 ← 2, 3 ← 3, 2 ← 0, and 0 ← 2 subbands. A rotational analysis yielded the rotational constants and quartic and sextic centrifugal distortion constants for both the $\text{A}\text{?}$ and $\text{X}\text{?}$ states and the band origin, with good precision. The molecular constants determined reproduce the observed transition frequencies with an average deviation of 0.0038 cm^?1. Small rotational perturbations in the excited state were found at J = 5, 6 and J = 10, 11 of J_1,J and at J = 15, 16 of J_2,J?1 levels.     

Millimeter-wave spectrum of the C4v molecule IOF5: l-type doubling of the kl = −1 transitions in the v11(E) = 1 state spectrum

Measurements of the rotational spectrum of the C_4v molecule IOF₅ are reported for the excited vibrational state v₁₁(E) = 1 for the transitions J13 ← 12, 14 ← 13, 16 ← 15, and 17 ← 16 (55–72 GHz) including the observation of the kl = −1 (q⁻), l-doubling effect. Detailed assignments of the E-state spectrum are presented based on the overlapping quadrupole structure. These data are analyzed together with earlier results for the excited vibrational state v₆(B₁) = 1 to give information concerning the ν₆(B₁)-ν₁₁(E) Coriolis interaction and the (Δl, Δk) = (2, 2) (q⁺) and (2, −2) (q⁻)l-resonance interactions. It is found that q₁₁⁻ = −2.57(10) MHz, |q₁₁⁺| = 0.094(20) MHz, Δ = ν₆ − ν₁₁ = 45.2(7) cm⁻, ζ_11,11^z = +0.18(1) and |ζ_6,11^y| = 0.73(4).     

The microwave spectrum of IF5 in excited vibrational states: Accidental degeneracy and avoided crossing of the kl = 3 and kl = −1 levels in the state v9(E) = 1

Measurements of the microwave spectrum of the C_4v molecule IF₅ in the excited vibrational states v₉(E) = 1 and v₅(B₁) = 1 are reported for the transitions J12 ← 11 and J13 ← 12 (65–72 GHz). The considerable spectral perturbations produced by an accidental degeneracy and avoided crossing of the ψ^? (kl = 3) and ψ^? (kl = ?1) levels of the v₉(E) = 1 state have been measured and analyzed. A spectroscopic determination of the axial rotation constant C₉ is reported and its implications for the molecular structure of IF₅ discussed.     

Inversion-rotation spectrum and spectroscopic parameters of 14ND3 in the ground state

The far-infrared spectrum of ¹⁴ND₃ has been recorded in the region between 30 and 220 cm^?1 at a resolution, before deconvolution, of approximately 0.004 cm^?1. ΔJ = +1, ΔK = 0, a ← s and s ← a inversion-rotation transitions have been measured and assigned up to J″ = 19. These transitions, the pure inversion-microwave transitions and ground-state combination differences from the analysis of the ν₂ and ν₄ bands have been fitted simultaneously to an inversion-rotational Hamiltonian which includes Δk = ±3 and Δk = ±6 interaction terms. The ground-state spectroscopic parameters obtained in this way reproduce the transition frequencies within the accuracy of the measurements.     

Stark spectroscopy of 13CD3OH with the HCN laser

The laser Stark spectrum of ¹³CD₃OH has been studied using the 311 μm line of the HCN laser. An extensive series of absorption lines has been observed and assigned to the J = 3 to 11 members of the K = 2 ← 3E₁, Q-branch transition in the v_t = 1 excited torsional state. Zero-field frequencies for all the assigned transitions are given with improved accuracy over those calculated from available molecular constants. For the Q-branch series, the branch origin and the series expansion coefficients are also presented.     

Study of the torsion-rotation Hamiltonian for symmetric tops using the millimeter wave spectrum of methyl silane

The torsion-rotation Hamiltonian for symmetric tops has been tested in methyl silane by combining recent anticrossing molecular beam measurements in the ground torsional state (v = 0) with pure rotational spectra taken for v as high as 4. The earlier microwave data set which consisted of J = 1 ← 0 and 2 ← 1 has been greatly extended by studying millimeter transitions for J = 4 ← 3, 5 ← 4, and 13 ← 12. An analysis of the 72 rotational frequencies for v ≤ 2 and the 15 anticrossing data for v = 0 yielded an excellent fit using 14 rotational, torsional, and distortion constants including the effective values for the A rotational constant and the barrier height V₃. No satisfactory fit could be obtained when the data set was extended to include measurements for (v = 3) or (v = 4). For each of these higher torsional levels, the difference between the observed frequencies and the predictions based on the best (v ≤ 2) constants can be expressed in terms of a shift δB_v in the B rotational constant, where δB_v is a smooth function of the torsional energy. This disagreement is of particular interest because it may result from the fact that the molecule passes from hindered to free rotation as v is increased from 2 to 4. The possibility of perturbation by a low-lying vibrational level is considered briefly. The information contained in the different types of spectra is discussed; the redundancy relations are treated and a Fourier expansion of the diagonal torsional matrix elements is introduced. For ¹²CH₃²⁹SiH₃, ¹²CH₃³⁰SiH₃, and ¹³CH₃²⁸SiH₃ pure rotational spectra for v = 0 were studied briefly in natural abundance. The results were combined with existing data for two deuterated symmetric rotors to obtain a structure based only on symmetric top rotational constants.     

Torsional bands of hydroxylamine

Infrared absorption spectrum of NH₂OH has been observed in its gaseous state, and the fine structures of the bands at 386 and 751 cm^?1 assignable, respectively, to the fundamental and overtone of the torsional vibration of this molecule have been examined. Band center frequencies for the n = 1 ← 0, 2 ← 1, 3 ← 2, 2 ← 0, and 3 ← 1 transitions (where n is the vibrational quantum number of the torsional oscillation) have been determined to be 386.2, 365.1, 346.3, 751.2, and 711.3 cm^?1, respectively. On the basis of these data, a discussion is given on the internal-rotation potential function.     

Microwave spectrum of CH3OD

The microwave spectrum of CH₃OD has been observed in the frequency region between 14 and 92 GHz. All the ground-state transitions with J ≤ 8 and J = 2 ← 1, a-type transitions in the excited torsional states (v = 1 and v = 2) have been observed. The spectrum has been analyzed and rotational constants, torsional constants, torsion-vibration-rotation interaction constants, and centrifugal distortion constants have been evaluated. The Stark effect measurements have been made and the dipole moment components have been determined as μ_a = 0.833 ± 0.008 D and μ_b = 1.488 ± 0.015 D.     

The two-dimensional anharmonic oscillator: The microwave spectrum of silyl isocyanate,SiH3NCO

The J + 1 ← J transitions (J = 2, 3, 4, 5, and 6) in the microwave spectrum of SiH₃NCO have been assigned for the vibrational ground state and for the vibrational states v₁₀ = 1, 2, and 3. The results for v₁₀ = 0 confirm earlier work. The vibration-rotation constants show a remarkable variation with v₁₀ and l₁₀. To a large extent the anomalous behavior of these constants has been explained in terms of a strongly anharmonic potential function for the ν₁₀ vibrational mode.     

Microwave spectrum of silyl fluoride: Coriolis resonance between ν2 and ν5 states

The J = 1 ← 0 and J = 2 ← 1 microwave rotational transitions of SiH₃F and SiD₃F have been measured for the ground and the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 vibrational states, for which the various rotational and vibration-rotation interaction constants have been obtained. Both molecules show an X-Y Coriolis resonance between the ν₂ and ν₅ vibrational states, whose separation are 29 and 8 cm^?1, respectively. In the case of SiD₃F the resonance is very strong and an exact numerical diagonalization of the energy matrix was employed.     

Laser magnetic resonance measurement of rotational transitions in the metastable a1Δg state of oxygen

Laser magnetic resonance (LMR) for five rotational transitions, J = 4 ← 3, 5 ← 4, 7 ← 6, 8 ← 7, 9 ← 8, of the oxygen molecule ¹⁶O¹⁶O in its metastable state, a¹Δ_g, v = 0, are observed using six fir laser lines. Taking the known values of the g factors, their zero-field frequencies are obtained as 340.0085(6), 424.9810(9), 594.870(1), 679.780(1), and 764.658(1) GHz, respectively. They are fit by $\text{(}\text{E}\text{h}\text{) = B}{}_0\text{[J(J + 1) ? 4] + D}{}_0\text{[J(J + 1) ? 4]}{}^2\text{+ (?1)}{}^{\mathrm{J}}\text{(}\text{1}\text{2}\text{)qJ (J + 1)[J(J + 1) ? 2]}$, where B₀ = 42.50457(10) GHz, D₀ = 153.14(110) kHz, and q = 0.050(90) kHz.     

Far infrared laser magnetic resonance spectrum of CH

Laser magnetic resonance spectra between 0 and 17 kG have been recorded and analyzed for $\text{(J′ ← J″) = (}\text{7}\text{2}\text{←}\text{5}\text{2}\text{)}$, $\text{(}\text{5}\text{2}\text{←}\text{3}\text{2}\text{)}$, and $\text{(}\text{3}\text{2}\text{←}\text{1}\text{2}\text{)}$ transitions in the CH molecule, using the optically pumped far infrared lasers: 118.8 μm (CH₃OH), 180.7 μm (CD₃OH), 554.4 μm (CH₂CF₂), 561.3 μm (DCOOD), and 567.9 μm (CH₂CHCl). Other transitions in CH were detected with the ¹³CH₃OH laser at 115.8, 149.3, and 203.6 μm. The CH radical was generated in a low-pressure methane and atomic fluorine flame within the laser cavity. Analysis of the M′_J ← M″_J structure yields wavenumbers for the rotational transitions mentioned above of 84.3494, 55.3397, and 17.8376 cm^?1, respectively. Combining results from the M_J analysis with the $\text{J =}\text{1}\text{2}\text{Λ-}\text{doubling}$ interval derived from radioastronomy measurements yields Λ-doubling values for the $\text{J =}\text{3}\text{2}\text{,}\text{5}\text{2}$, and $\text{7}\text{2}$ states of 0.0237, 0.1620, and 0.3759 cm^?1, respectively. Both the rotational intervals and the Λ-doublings are in good agreement with earlier less precise optical results. Analysis of the hyperfine structure yields values for the Frosch and Foley hyperfine parameters of a = +52, b = ?74, c = +52, and d = +43.6 MHz, in good agreement with recent ab initio estimates and radioastronomy measurements.     

Pressure broadening of millimeter lines of carbon monoxide

We report measurements on self-, N₂-, O₂-, and He-broadened widths of the 230-GHz line of carbon monoxide. The temperature dependence of the broadening parameters has been studied in the range 220–300 K. The results are compared with values previously obtained for the 115-GHz line and with published infrared data on the J = 1 ← 0 and J = 2 ← 1 transitions of carbon monoxide.     

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.