Laser Stark spectroscopy of thioformaldehyde in the 10-μm region: The ν3, ν4, and the ν6 fundamentals

The ν₃, ν₄, and ν₆ bands of thioformaldehyde, H₂CS, have been studied using the technique of laser Stark spectroscopy. The H₂CS was produced by the pyrolysis of dimethyl disulfide, and the spectrum was observed using a multipass absorption cell. The band origins are ν₃, 1059.2037 cm^?1; ν₄, 990.1866 cm^?1; and ν₆, 991.0149 cm^?1. The band previously assigned as 2ν₆ has been reassigned as 2ν₂, leading to a value of the ν₂ band origin of ca. 1439 cm^?1. Rotational constants and dipole moments of the vibrational states have been determined.     

Microwave study of vibration-rotation spectrum of carbon suboxide C3O2 in the 300- to 1000-GHz frequency range

The submillimeter wave spectrum of the C₃O₂ molecule was investigated within the 300- to 1000-GHz range. The measured frequencies include 256 lines belonging to the ground vibrational state and to four excited vibrational states of ν₇. Rotational and centrifugal constants and constants of “?” splitting for the ground and excited states ν₇¹, 2ν₇², 3ν₇³, 4ν₇⁴ as well as frequencies of purely vibrational transitions ν₇¹ ← 0; 2ν₇² ← ν₇¹; 3ν₇³ ← 2ν₇²; 4ν₇⁴ ← 3ν₇³ together with their correlation matrix were determined.     

Laser-radiofrequency double-resonance spectroscopy of 13CH3I

Pure quadrupole resonances of the I¹²⁷ nucleus of ¹³CH₃I have been observed using laser-radiofrequency double resonance. Quadrupole coupling constants are reported for the ground, ν₃, 2ν₃, ν₆, 2ν₆, ν₃ + ν₆, and 2ν₃ + 2ν₆ states. Smaller hyperfine constants are also reported for the ground and ν₆ states.     

Fourier transform infrared spectra of H2CS and D2CS

Infrared spectra of thoformaldehyde, H₂CS and D₂CS, were observed in the gas phase at a resolution of better than 0.1 cm^?1 from 4000 to 400 cm^?1 using a Nicolet FTIR system. Vibrational band origins and rotational constants were determined for ν₂, ν₃, ν₄, and ν₆ of H₂CS and for ν₁, ν₂, ν₃, ν₄, and ν₆ of D₂CS. The ν₃, ν₄, and ν₆ bands of H₂CS were analyzed as a set of three Coriolis interacting bands, and three Coriolis constants were determined; similarly the ν₄ and ν₆ bands of D₂CS were analyzed as a pair of interacting bands and one Coriolis constant was determined. A general harmonic force field was determined, without constraints, to fit the vibrational wavenumbers, Coriolis constants, and centrifugal distortion constants. A zero-point (r_z) structure was determined from the ground-state rotational constants, and the equilibrium (r_e) bond lengths were estimated.     

Microwave spectrum of methylene fluoride-d2, CD2F2 in the excited vibrational states

The rotational spectra of ¹²CD₂F₂ in the ν₂, ν₃, ν₄, 2ν₄, ν₅, ν₇, ν₈, and ν₉ states were observed and assigned. Weak Coriolis interactions between ν₃ and ν₇, ν₃ and ν₉, and ν₅ and ν₇ were analyzed using approximate expressions for the rotational energy levels. The resonance between the ν₂ and the ν₈ state was found much stronger, and an effective two-dimensional Hamiltonian with the Coriolis term in the off-diagonal block was set up to analyze the spectra. The effect of the Fermi resonance between ν₃ and 2ν₄ was found to be very small.The ground-state spectrum of ¹³CD₂F₂ was observed and the rotational constants and the centrifugal distortion constants were determined. The data on ¹²CD₂F₂ and ¹²CDHF₂ were also improved very much in accuracy.The Coriolis coupling constants and the differences between two vibrational levels in resonance, which were determined by the analysis of the satellite spectra, are in good agreement with those obtained from vibrational spectra, except for the ν₂ band center, which is revised to 1170.3 cm^?1. The force constants were also checked using the centrifugal distortion constants of ¹²CD₂F₂, ¹³CD₂F₂, and ¹²CHDF₂.     

The 2ν2, ν1 and ν3 bands of D216O. The ground state (000) and the triad of interacting states {(020), (100), (001)}

Three spectra of D₂¹⁶O between 2170 and 3090 cm^?1 have been recorded with a Fourier transform spectrometer having a resolution of about 5 × 10^?3 cm^?1. A careful analysis of the bands 2ν₂, ν₁, and ν₃ has led to a largely extended and more precise set of rotational levels belonging to the vibrational states (000), (020), (100), and (001). From this set, we have then been able to determine improved rotational constants for the ground state (000) and precise vibrational energies, rotational and coupling constants for the three interacting states (020), (100), and (001). The Fermi-type interaction between (020) and (100) as well as the Coriolis-type interactions between (100) and (001) and between (020) and (001) have been explicitly taken into account. Many vibrorotational resonances were detected and are discussed.     

Supersonic free-jet quantum cascade laser measurements of ν4 for CF3Cl and CF3Cl and FTS measurements from 400 to 1260 cm

A supersonic free-jet spectrum of the ν₄ band of CF₃Cl has been measured using a quantum cascade laser system. Those measurements were combined with a low temperature (−67 °C) FTS spectrum of the region 1060-1260 cm⁻¹ and with room temperature FTS measurements down to 400 cm⁻¹ to give improved values for the rovibrational constants for the ν₁, ν₂, ν₃, 2ν₃, 2ν₅, ν₄, and ν₅ states of CF₃³⁵Cl and CF₃³⁷Cl. The principal perturbation found by earlier investigators in the ν₁ band is treated as a very weak Coriolis interaction at several avoided crossings of the rotational levels of the ν₁ state and the 2ν₅ state with kl < 0. None of the other vibrational states showed any signs of perturbations. With these new measurements we now have high resolution data on all of the fundamental vibrational states except ν₆.     

The 2ν1 + ν3 and 3ν3 bands of 14N16O2

The spectra of the 2ν₁ + ν₃ and 3ν₃ bands of ¹⁴N¹⁶O₂ have been recorded by means of high-resolution Fourier transform spectroscopy and have been extensively analyzed. The (2 0 1) and (0 0 3) rotational levels deduced from the analysis have been reproduced within the experimental uncertainty using a Hamiltonian which takes into account the Coriolis interaction coupling the vibrational states of the diads {(2 2 0), (2 0 1)} and {(0 2 2), (0 0 3)}. Finally, precise sets of vibrational energies, and spin-rotation, rotational, and coupling constants have been derived for these vibrational states.     

Microwave spectrum of nitrogen dioxide in excited vibrational states—Equilibrium structure

Microwave spectra were observed for ¹⁴NO₂ in the vibrationally excited ν₁, ν₂, ν₃, and 2ν₂ states, as well as for ¹⁵NO₂ in the ν₁ and ν₂ states. The rotational constants, spin-rotation coupling constants and hyperfine interaction constants were precisely determined. Second-order change of the spin-rotation coupling constants with respect to the bending vibrational quantum number v₂ was also determined. Combined use of the rotational constants obtained by the present microwave investigation and those reported in high-resolution infrared spectroscopic studies leads to the determination of all the vibration-rotation interaction constants α_s and γ_ss′ and the equilibrium structure of nitrogen dioxide, $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{N}\text{O) = 1.19389 ± 0.00004}\text{A}\text{?}$ and θ_e (ONO) = 133°51.4′ ± 0.2′, in the second-order approximation with respect to the vibrational quantum numbers.     

Millimeter wave spectroscopy of OCS in vibrationally excited states

The millimeter wave transitions of OCS in the range of J = 9-8 to 12-11 were measured with an accuracy of 10 kHz for the vibrational states 2ν₂, 3ν₂, 4ν₂, ν₁, ν₁ + ν₂, ν₁ + 2ν₂, and ν₁ + 3ν₂ of the normal species and ν₂, 2ν₂, and 3ν₂ of OC³⁴S. An anomalous behavior of the centrifugal distortion constant was observed and interpreted as due to the l-type resonance between the sublevels with different l values. The unperturbed values of the centrifugal distortion and l-type doubling constants and the vibrational intervals between sublevels were determined.     

The high resolution infrared spectrum of the 2ν2 + ν3 and ν1 + ν2 + ν3 bands of 14N16O2: Vibration and vibration-rotation constants of the electronic ground state of 14N16O2

The A-type bands, 2ν₂ + ν₃ and ν₁ + ν₂ + ν₃, with band centers at 3092 and 3638 cm^?1, respectively, of ¹⁴N¹⁶O₂ have been measured with resolution of 0.03 cm^?1 or better. Spectroscopic constants have been derived for the upper states of both bands. Infrared determined band constants have been combined with laser-excited resonance fluorescence data to obtain a set of vibration and vibration-rotation constants for the ground state of ¹⁴N¹⁶O₂.     

A High-Resolution Analysis of the ν3 Absorption Band of Trifluoromethane

A high-resolution (up to 0.0018 cm⁻¹ unapodized) room temperature mid-infrared (650 to 750 cm⁻¹, 13.3 to 15.4 μm) absorption measurement of the ν₃ vibrational band of trifluoromethane (fluoroform, CHF₃, HFC-23) vapor was made with a Fourier transform spectrometer. A rovibrational analysis of over 1400 infrared transitions of the ν₃ band has yielded rotational constants, including sextic centrifugal distortion constants. The results are compared with two previous analyses of microwave and infrared spectra. The line positions of the lower J parts of the ν₃+ν₆−ν₆ and 2ν₃−ν₃ hot bands have been identified and constants obtained for the 2ν₃ state. The central Q branch and a few unblended transitions of the ν₃ band of ¹³CF₃H have been identified and the band origin has been determined. The relative intensities of the ν₃ band together with the 2ν₃−ν₃ hot band and ν₃ band of ¹³CF₃H have been calculated using the constants derived from this work.     

The vibration-rotation spectrum of DCP: The analysis of the fundamental bands ν1 and ν2, of the overtone band 2ν1, of the summation band ν1 + 2ν3, and of the difference band ν1 - ν2

The vibration-rotation bands ν₁, ν₂, ν₁ - ν₂, ν₁ + 2ν₃, and 2ν₁ have been recorded and analyzed. A simultaneous fit of 395 transitions, including those previously known, was made to obtain improved spectroscopic constant for D¹²CP in 6 different vibrational states.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.     

Microwave spectrum of methylene fluoride in excited vibrational states

The rotational spectra of ¹²CH₂F₂ in seven of the nine fundamental vibrational states and also in overtone and combination states involving the ν₄ mode were observed and assigned. Coriolis interactions between ν₃ and ν₇, ν₂ and ν₈, ν₃ and ν₉, and ν₅ and ν₇ were analyzed by using approximate expressions for the rotational levels. An effective Hamiltonian with the Coriolis term in the off-diagonal block was applied to stronger interaction between ν₃ and ν₉. Fermi resonance between ν₃ and 2ν₄ was found to be negligible. The ground state spectra of ¹²CH₂F₂ and of ¹³CH₂F₂ were remeasured to improve the accuracy of the rotational and centrifugal distortion constants. The Coriolis coupling constants and the energy differences between two vibrational levels in resonance, which were obtained through an analysis of the satellite spectra, are compared with the results derived from a normal coordinate analysis.     

The rotational spectra of the 79, 69, and 7 vibrational states of nitric acid

The rotational spectra of the first three vibrational states of nitric acid above 1000 cm⁻¹, 7¹9¹, 6¹9¹, and 7², have been measured and analyzed. The 7² state, along with the previously published 7¹ state, show the rotational and centrifugal distortional constants have a near linear dependence on the υ₇ vibrational quantum number. Large changes for several centrifugal distortion constants of the υ₇ = n series of states are attributed to a c-type Coriolis resonance manifold between the ν₇ and ν₆ vibrational modes and the Hamiltonian reduction and representation used to fit the spectra. The 7¹9¹ and 6¹9¹ states have torsional splittings of 12.361(8) and 22.47(1) MHz, respectively. These splittings are large compared to 2.340(8) MHz of the 9¹ state and can be explained by a ∼1-2% mixing through anharmonic Fermi resonances with the 9³ state, which has a large torsional splitting of ∼1760 MHz. The millimeter/submillimeter-wave spectrum of each state was fit separately to the experimental uncertainty of the measurements. The resultant rotational constants, distortional constants and inertial defects agree well with DFT calculations.     

Subject index for volume 100

The ν₂ fundamental band of HNCO has been observed for the first time under a resolution of 0.015 cm^?1. The band origin for this NCO antisymmetric stretching vibration is found to be at 2268.893 cm^?1, rather distant from the previously reported value of 2274 cm^?1. Nineteen subbands have been analyzed and term values for both ground and ν₂ states with K up to 4 have been obtained. Effective rotational constants B and centrifugal distortion constants D and H have also been determined. Interactions are observed with 2ν₄ + ν₅ and ν₃ + ν₄. Large perturbations are observed for K = 0 and K = 1 levels of ν₂. Transitions are also seen for three other vibrations, ν₄ + ν₅ + ν₆, ν₃ + ν₆, and 2ν₄ + ν₆.     

Carbon suboxide as a quasilinear molecule with a large amplitude bending mode: Determination of the molecular constants and the ν7 potential function

The model of a quasilinear molecule with a large amplitude bending mode is used to treat C₃O₂. The Hamiltonian operator, including the rotation-vibration interaction, is derived allowing only a single vibrational degree of freedom, namely, the ν₇ mode corresponding to the bending at the central carbon atom. The CCO angle is constrained to be 180°. With this model the rotational energy levels and, thus, the molecular constants can be computed for any ν₇ level once the ν₇ potential is specified. The l-doubling is included only for π states. The model contains three adjustable parameters: the rotational constant in the linear configuration and two terms in the potential function, and these are determined by fitting three experimental quantities: the rotational constants in and the separation between the ground and 2ν7⁰ states. The resulting ν₇ potential has a 30.56 cm^?1 barrier at α = 0 with a minimum at α = 11.04°, where 2α is the angular deviation from linearity. The model gives a good fit to the 2ν₇ Raman data and to the rotational and centrifugal distortion constants in all of the nν7^l states which have been analyzed. A similar analysis is applied with equal success to the states with ν₄, the asymmetric CC stretch mode at 1587 cm^?1, simultaneously excited with a ν₇ mode. The potential in this case has a 56.58 cm^?1 barrier at α = 0 with a minimum at α = 13.02°.     

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.     

Infrared-microwave two-photon spectroscopy of the ν4 and ν6 bands of D2CO

Transitions in the ν₄ and ν₆ bands of D₂CO have been recorded by means of an infrared-microwave two-photon spectometer. The two-photon frequencies have been combined with frequencies obtained by infrared laser Stark and microwave spectroscopy to obtain rotational and centrifugal distortion constants for the ground, ν₄, and ν₆ states as well as vibrational frequencies and the Coriolis coupling constant for the two excited states. Expressions are reported for the linestrengths of two-photon transitions for an asymmetric rotor for the cases of parallel and perpendicular orientation of the planes of polarization of the infrared and microwave radiation.