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.     

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.     

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.     

ΔK = 2 transitions in H2CO and D2CO

Weak transitions of the type ΔJ = ± 1, $\text{Δ}\text{K}{}_{\mathrm{a}}\text{= ? 2}$, ΔK_c = ± 3 have been observed in H₂CO and D₂CO by the millimeterwave double resonance method and also by direct absorption with a Stark modulated spectrometer. The addition of these new transitions in a least-squares analysis, in which all previously known microwave and millimeterwave data are also included, results in an improved set of rotational and distortion constants.     

Collisional transfer of rotational energy in the 2B1 electronic state of nitrogen dioxide

Collisional satellite lines have been observed in fluorescence from nitrogen dioxide excited by the 4545-Å line of the argon laser. The 13_0,13 level of the (0, 8, 0) vibrational state is populated by the laser and undergoes collisionally induced transitions to the 11_0,11, 15_0,15, and 17_0,17 states. These collisionally populated states are identified by their fluorescence to the well-studied (0, 0, 0) and (0, 1, 0) levels of the ground electronic state. These satellite lines are also observed in fluorescence to the (0, 2, 0) and (0, 3, 0) vibrational levels of the ground electronic state. The wavenumbers of those lines, together with those from unrelaxed fluorescence and previously published microwave transitions, allow vibrational and rotational constants for the higher vibrational states to be determined more accurately than was previously possible. Several much weaker forbidden transitions have also been observed, including ΔK_a = 0 through ?6 transitions in the (0, 8, 0)-(0, 0, 1) band.     

Analysis of the ν9 and ν10 bands of cyclopropane

The infrared spectrum of gaseous cyclopropane has been measured in the regions 980–1080 and 1400–1500 cm^?1, containing the ν₁₀ and ν₉E′ fundamental bands, respectively, using a high-resolution Fourier transform instrument. Deconvolution was used to enhance the resolution in the crowded parts of the spectrum to ～0.0020–0.0025 cm^?1. Apart from the rotational l-resonance affecting mainly the low-K subbands, the ν₉ band is strongly perturbed by Fermi resonance with the 2ν₁₄² state lying ～41 cm^?1 above. The effects of the Fermi resonance are most pronounced in the high-KΔK = +1 subbands as the 2ν₁₄^?2 levels would cross the ν₉⁺ levels near K = 30. ^rR lines of 2ν₁₄^?2 for K = 24 to 36, enhanced by the resonance, have been identified in the region 1469–1475 cm^?1 of the spectrum. Two extra perturbation-enhanced subbands are found adjacent to the K = 16?17 and K = 17?16 subbands of ν₉: these have been ascribed to the K = 18?17 transitions in 2ν₁₄^?2 and to the K = 19?16 transitions in $\text{ν}{}_2\text{2ν}{}_{14}{}^0$, respectively, as their upper states coincide with the corresponding levels ν₉^?(K = 16) and ν₉⁺(K = 17). A combination of l-resonance and Fermi resonance is mainly responsible for the interactions causing the perturbations and appearance of the extra subbands, but a direct rotational interaction 〈ν₉^?(K)|h₃|2ν₁₄^?2(K + 2)〉 also had to be introduced to accurately account for the observations. In contrast, the ν₁₀ band is not appreciably perturbed by other states and merely exhibits effects of strong l-resonance in the low-K subbands, and K-doubling of the high-J lines of the K = 2–3 subband. A detailed analysis of the spectrum and of the perturbations is described and sets of accurate spectroscopic constants are reported for ν₁₀ and ν₉ as well as for the perturbing state 2ν₁₄², which reproduce 3020 observed lines of the ν₁₀ band with a standard deviation of 0.0008 cm^?1 and 1810 lines of ν₉ with a standard deviation of 0.0010 cm^?1.     

Millimeter wave spectrum of acetonitrile oxide,CH3CNO,in the ν10 vibrational manifold: The ground state and the state v10 = 1

The pure rotational spectrum of CH₃CNO was measured in the frequency range 75 to 230 GHz. For the ground state, transitions were measured for J between 9 and 28 and for K from 0 to 12. In the v₁₀ = 1 state the measurements range from J = 0 to 19 and from K = 0 to 11. Numerous perturbations are observed, apparently due to accidental resonances with levels in other vibrational states. The contributions due to ΔK = 2, Δl = 2 matrix elements (l-type resonance and l-type doubling) are accounted for by matrix diagonalization, and the effects due to accidental resonances are presented graphically.     

Measurement of the dipole moment of CF3CN

The Stark effect was observed for K = 0 and K = 1, J = 1 → 2 transitions in CF₃CN. Measurements were made in a Stark modulated microwave spectrometer. The dipole moment obtained was μ = 1.262 ± 0.010 D. An analysis of the effects of electric field inhomogeneities on the observed Stark shifts for K = 0 and K = 1 states is included. Appropriate corrections are given for measuring linear Stark effects in a standard waveguide cell calibrated using a molecule with second-order Stark effect.     

The Rotational Spectrum of ClClO2 in Its v4=1 and v6=1 Vibrationally Excited States: An Example of Strong Coriolis Interaction

The two lowest vibrational states of ³⁵Cl³⁵ClO₂, v₄=1 (A′) and v₆=1 (A″), were investigated between 223 and 500 GHz. More than 250 rotational transitions were recorded with J and K_a up to 71 and 34, respectively. The spectra are heavily perturbed by strong c-type and weaker a-type Coriolis interactions. Near degeneracies of rotational levels of the two vibrational states having ΔJ=0, ΔK_a=5 to 1, and ΔK_a+ΔK_c= odd cause moderate to severe perturbations in the rotational structure, preventing the states from being fit as isolated ones. Distortions in the hyperfine structure facilitated the assignment of rotational quantum numbers. Several resonantly interacting levels with ΔK_a=5 to 2 were accessed, and a number of transitions between the states were observed. While resonant Coriolis interaction with ΔK_a=1 occurs only at K_a>40, the effects of this interaction are so severe that nonresonant interaction considerably perturbs the highest K_aQ-branches observed. The observed transitions could be fit to within experimental uncertainties employing the first-order Coriolis coupling constants fixed to those from the harmonic force field, sextic distortion constants fixed to those of the ground state, and some higher order Coriolis terms. The energy difference calculated from the fit agrees well with that obtained from the matrix-isolation infrared spectrum. Quadrupole coupling constants were determined for both Cl nuclei and both vibrational states.     

A new joint analysis of the ground and first excited torsional states of methylformate

A global fit within experimental accuracy of microwave rotational transitions in the ground and first excited torsional states (v_t = 0 and 1) of methylformate (HCOOCH₃) is reported, which combines older measurements from the literature with new measurements from Kharkov. In this study the so-called ‘‘rho axis method’’ that treats simultaneously both A and E species of the ground and first excited torsional states is used. The final fit requires 55 parameters to achieve an overall unitless weighted standard deviation of 0.71 for a total of 10533 transitions (corresponding to 9298 measured lines) with rotational quantum numbers up to J ? 62 and K_a ? 26 in the ground state and J ? 35 and K_a ? 23 in the first excited torsional state. These results represent a significant improvement over past fitting attempts, providing for the first time a fit within experimental accuracy of both ground and first excited torsional states.     

Infrared-microwave double resonance of propynal by using the 3.51 μm HeXe laser

The 3.51 μm HeXe laser is magnetically tuned over a wavenumber of 0.2 cm^?1 and used for infrared absorption and double resonance spectroscopy. Eight rotation-vibration lines of propynal in the ν₂ band are assigned by the Stark effect. Eleven microwave transitions in the v₂ = 1 vibrational state are observed by the method of infrared-microwave double resonance. The rotational constants of the excited state and the band origin of the vibration ν₂ are determined from the observed spectra.     

The far-infrared spectrum and spectroscopic parameters of PH3 in the ground state

The far-infrared spectrum of phosphine, PH₃, was recorded in the region between 30 and 200 cm⁻¹ at a resolution of 0.002 cm⁻¹. ΔJ = +1, ΔK = 0 rotational transitions in the ground state were measured and assigned up to J″ = 22 and K = 19. These transitions were analyzed together with the presently available microwave and submillimeter-wave data on the basis of different formulations of the rotational Hamiltonian, which included Δk = ±3 and/or Δk = ±6 interaction terms. An upper limit for the constant of the inversion splitting was obtained by fitting the same transitions to an appropriate inversion-rotational Hamiltonian. Rotational transitions in the v₂ = 1 and v₄ = 1 vibrational states were also observed.     

The ν2 and ν4 bands of AsH3

The infrared absorption of arsine, AsH₃, between 750 and 1200 cm^?1 has been recorded at a resolution of 0.006 cm^?1. Altogether 2419 transitions, including nearly 700 “perturbation allowed” transitions with Δ∥k ? l∥ = ±3, ±6, and ±9, have been assigned to the ν₂(A₁) and ν₄(E) bands. Splitting of the transitions for K″ = 3, 6, and 9 was also observed. To fit the rotational pattern of the v₂ = 1 and v₄ = 1 vibrational states up to J = 21, all the experimental data were analyzed simultaneously on the basis of a rovibrational Hamiltonian which took into account the Coriolis interaction between ν₂ and ν₄ and also included several essential resonances within them. The derived set of 38 significant spectroscopic parameters reproduced the 2328 transition wavenumbers retained in the final fit within the accuracy of the experimental measurements.     

Microwave fourier transform spectroscopy of pure rotational ν4 ↔ ν4 transitions and reanalysis of the ν2ν4 dyad of methane-d4

Pure rotational transitions of a spherical top in a degenerate vibrational state have been observed directly for the first time with the help of pulsed microwave Fourier transform (MWFT) spectroscopy. Twelve rotational transitions in the v₄ = 1 vibrational excited state of CD₄ have been identified. The theoretical basis for the transition moments has been developed and the line strengths of the rotational transitions have been estimated. The measured rotational transition frequencies have been included in a reanalysis of the data from a previously recorded high-resolution FTIR spectrum of the ν₂ and ν₄ bands. The v₄ = 1 state of CD₄ is strongly coupled to the v₂ = 1 state by Coriolis interaction. Thirty molecular parameters of the $\text{ν}{}_2\text{ν}{}_4$ dyad have been fitted finally from the combined microwave and infrared data. The microwave data are reproduced with a standard deviation of 42 kHz, and the infrared data with a standard deviation of 0.0002 cm^?1; in each case, this is close to the estimated experimental prescision.     

Laser-induced fluorescence from antimony dimers

Antimony dimers in the vapor phase were studied by the technique of laser-induced fluorescence. In addition, collision-induced rotational transitions were observed. Two new states labeled K and K′ were identified in the 32 000-cm^?1 region, for one of them the vibrational and rotational constants could be determined. A spectroscopic analysis was also performed for the B → X system.     

“Forbidden” millimeter-wave transitions in arsine

A millimeter-wave spectrometer having a sensitivity of 4 × 10^?10 cm^?1 in the 2-mm region has been used for observation of the “forbidden” transitions J → J, K = ±4 → ±1 and J → J, K = ±5 → ±2 in AsH₃. A comprehensive computer analysis was made of the frequencies measured in this work together with available microwave frequencies of other transitions. This analysis provides accurate values of the rotational constants, nuclear quadrupole couplings, and effective structural parameters of the molecule. The spectral constants B₀ and C₀ (in MHz) are 112 470.597 and 104 884.665, respectively.     

Microwave spectrum of silicon difluoride in the excited vibrational states,equilibrium structure,anharmonic potential function,and ν1-ν3 Coriolis resonance

The microwave spectrum of SiF₂ was identified in the excited states of the stretching vibrations. It was found that the Coriolis resonance between the v₁ = 1 and v₃ = 1 vibrational states has perturbed very much the spectra of these states. An extensive analysis of the Coriolis resonance gave a very accurate value of the difference between the ν₁ and ν₃ fundamental frequencies, ν₁ - ν₃ = ? 15.395 ± 0.001 cm^?1 and, thus, gave a strong basis to the assignment of the stretching modes by Khanna et al. An intervibrational-state transition, v₁ = 1, 8₅₄ ← v₃ = 1, 8₁₇ was identified.The observed rotational constants in the v₁ = 1 and v₃ = 1 states were combined with those in the ground and v₂ = 1 states by Rao and Curl to obtain the equilibrium structure, harmonic force constants and complete sets of the cubic and the third-order potential constants.     

Analysis of the ν6 band of 12CH3D at 8.6 μm

The ν₆(E) fundamental vibration-rotation band of monodeuteromethane (¹²CH₃D) has been recorded in the spectral range 1033–1270 cm^?1 with a resolution of approximately 0.04 cm^?1. Of the 669 transitions with J′ ≤ 17 identified, 633 have been retained for the determination of the rotational levels in the upper state v₆ = 1. The Coriolis interaction between the v₆ = 1(E) and v₃ = 1 (A₁) vibrational states of ¹²CH₃D results in large A₁A₂ splittings of levels with v₆ = 1 and |K ? l₆| = 0 or 3; the mixing in K and l₆ also gives rise to some ten forbidden transitions observed in the spectra. These effects have been very well explained within the formulation based on the contact transformation method. Values of 15 molecular structure constants of the v₆ = 1 state have been determined from a least-squares analysis of the 633 retained transitions. These constants can be used to estimate values of the upper-state energies up to fourth order, and through them the spectral positions of the 633 retained transitions are reproduced with an overall standard deviation of 0.013 cm^?1, which is within experimental uncertainties.     

Molecular beam electric resonance study of KCN,K13CN and KC15N

The microwave spectra of the isotopic species K¹³CN and KC¹⁵N have been investigated by molecular beam electric resonance spectroscopy, using the seeded beam technique. For both isotopic species about 20 rotational transitions originating in the ground vibrational state were observed in the frequency range 9–38 GHz. The observed transitions were fitted to an asymmetric rotor model to determine the three rotational, as well as the five quartic and three sextic centrifugal distortion constants. The hyperfine spectrum of KCN has been unravelled with the help of microwave-microwave double-resonance techniques. One hundred and forty hyperfine transitions in 11 rotational transitions have been assigned. The hyperfine structures of K¹³CN and KC¹⁵N were also studied. For all three isotopic species the quadrupole coupling constants and some spin-rotation coupling constants could be deduced. The rotational constants of the ¹³C and ¹⁵N isotopically substituted species of potassium cyanide, combined with those of the normal isotopic species (determined more accurately in this work), allowed an accurate and unambiguous evaluation of the structure, which was confirmed to be T shaped. Both the effective structure of the ground vibrational state and the substitution structure were evaluated. The results for the effective structural parameters are $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.169(3)}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>KC</mtext>}}\text{= 2.716(9)}\text{A}\text{?}$, and $\text{r}{}_{\mathrm{<mtext>KN</mtext>}}\text{= 2.549(9)}\text{A}\text{?}$. The values obtained for the principal hyperfine coupling constant eQq_z(N), the angle between the CN axis and z_N, and the bond length r_CN indicate that in gaseous potassium cyanide the CN group can be considered as an almost unperturbed CN^? ion.     

The microwave spectrum of trioxaadamantane

The microwave spectrum of 2,8,9-trioxaadamantane has been investigated in the region from 12.4 to 26.5 GHz. The observed spectrum exhibited the expected symmetric top pattern, with the rotational constant B₀ = 1848.64 MHz. Numerous weaker lines were observed and were attributed to vibrational satellites of the main rotational transition. The transitions from J = 3 → 4 through J = 6 → 7 were studied and no centrifugal distortion effects were observed.A structure is derived that is consistent with the observed rotational constants of the normal and one isotopic species by use of the method of diagnostic-least-squares.The second order stark effect for the K = 0 state yielded a dipole moment of 3.01 ± 0.03 D.