Stark modulation infrared diode laser spectroscopy of the ν6 + ν8 band of diacetylene

The infrared diode laser spectrum of the ν₆ + ν₈ band of diacetylene (HCCCCH), i.e., a combination band of symmetric π_g (ν₆) and antisymmetric π_u (ν₈) CCH bending vibrations, was recorded by the Stark and source modulation techniques. The analysis of the Stark modulation spectrum allowed us to locate the 2ν₆ (Σ_g⁺) and 2ν₈ (Σ_g⁺) vibrational states, which are inaccessible by infrared transitions from the ground state. It is also shown that the Stark modulation spectrum can be used to confirm the rotational assignment of the ν₆ + ν₈ band.     

Microwave vibration rotation spectrum of diacetylene

Microwave spectrum of diacetylene (HCCCCH) arising from vibration-rotation transitions between closely lying excited vibrational states was observed. The ν₈-ν₆ band which has been reported in our previous paper was reinvestigated in a frequency region extended to 175 GHz, where ν₆ and ν₈ respectively represent the symmetric (π_g) and antisymmetric (π_u) CCH bending vibrations. The ν₈ + ν₉ ? ν₆ ? ν₉ band, where ν₉ is the lowest frequency (220 cm^?1) bending mode with π_u symmetry, was newly identified. Precise molecular constants associated with the ν₈ - ν₆ band and the three subbands Σ_g⁺ - Σ_u⁺, Σ_g^? - Σ_u^?, and Δ_g - Δ_u of the ν₈ + ν₉ ? ν₆ ? ν₉ band were determined by least-squares analyses. l-Type resonance interactions in the ν₆ + ν₉ and ν₈ + ν₉ vibrational states were analyzed. Also, a Fermi resonance which perturbs the Σ_g⁺ substate of the ν₈ + ν₉ state was discussed. The transition dipole moments were determined from the Stark effect for the Σ_g⁺ - Σ_u⁺ and Σ_g^? - Σ_u^? subbands of ν₈ + ν₉ ? ν₆ ? ν₉.     

The ν7 vibrational states of C3O2: A least-squares fit of the rigid-bender model to the v7ν7l7 energies and rotational constants

The rigid-bender model is used to treat the large-amplitude, low-frequency, bending vibration ν₇ of C₃O₂. Different parameterizations of the bending potential function are considered, and a simple two-term power series is found to give the best fit. With this parameterization, using a least-squares fit to energies and B values, the ν₇ potential function is determined for the ground state as well as for the states in which ν₂, ν₃, ν₄, ν₆, 2ν₆, ν₁ + ν₃, ν₁ + ν₄, ν₂ + ν₃, and 2ν₂ + ν₄ are excited. The excitation of other vibrations has in some cases a drastic effect on the ν₇ potential. In the ground state the potential has a 29 cm^?1 barrier at the linear position, in ν₁ + ν₃ the barrier increases to 79 cm^?1, while in 2ν₂ + ν₄ the barrier vanishes. An equilibrium potential is determined by correcting the ground state potential for the effects of zero-point motion of the normal vibrations ν₁, …, ν₆. This potential has a 35.6-cm^?1 barrier with a minimum at α = 11.14°, where 2α is the angular deviation from linearity. The model accurately predicts the quartic and sextic centrifugal distortion terms for the low-lying v₇ν₇^l₇ states. Second-order l-type coupling is included in the calculations of the quartic terms. The effects of this coupling, which are most pronounced for the ν₇ ≥ 2 states, adequately explain the negative D term recently reported for the ν₂ + 4ν₇⁰ state.     

Infrared spectra of 1-phosphapropyne,CH3CP,and its perdeuteride,CD3CP

The infrared spectra of 1-phosphapropyne, CH₃CP, and its perdeuteride, CD₃CP, have been measured in the gaseous and solid states. The Q_K branches of perpendicular bands have been analyzed in terms of the usual quadratic expression in K. Fermi resonances were identified for the ν₁, ν₂ + ν₃, 2ν₃, 2ν₆⁰; and ν₅, 2ν₃ + ν₈ band systems of CH₃CP and the ν₁, 2ν₃, 2ν₆⁰; ν₆, ν₇ + ν₈; and ν₇, 3ν₈¹ band systems of CD₃CP. The xy Coriolis interaction was also identified between the ν₃ and ν₆ bands of the two species. All the fundamentals were assigned and the normal coordinate treatment was carried out along with the Coriolis constants, ζ^z.     

Diode laser spectrum of HCCl near 5 μm: The ν2 fundamental and accompanying hot bands

The CC stretching band ν₂ of iodoacetylene has been studied by tunable laser spectroscopy in the range of 2037–2071 cm^?1. The hot bands associated with the low-lying bending vibrations ν₄ and ν₅ were observed. For the Π-Π hot bands, the splitting caused l-type doubling was resolved for high J transitions. For the fundamental band the hyperfine splittings due to the ¹²⁷I nuclear quadrupole moment were clearly observed for R(0) and P(1) transitions. Combination of these diode laser spectra with the microwave data allows precise determination of the constants in the ground and excited vibrational states.     

Laser Stark and laser microwave double-resonance spectroscopy of deuterated fluoroacetylene with the CO2 laser

The CO₂ laser Stark spectrum of deuterated fluoroacetylene was identified with the aid of the double-resonance technique for the ν₃, ν₃ + ν₅ ? ν₅, ν₃ + ν₄ ? ν₄, ν₃ + 2ν₅ ? 2ν₅, and ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅ vibrational bands. Laser microwave double-resonance signals were observed in the presence of the Stark field. From the analysis of the double-resonance signals precise values of the dipole moment were obtained for 10 vibrational states, in Debye, with the uncertainties in parentheses: ground, 0.73292(22); ν₅, 0.75656(17); ν₄, 0.68412(24); 2ν₅(Σ⁺), 0.78063(21); ν₄ + ν₅(Σ⁺ or Σ^?), 0.70698(19); ν₃, 0.75772(30); ν₃ + ν₅, 0.78270(18); ν₃ + ν₄, 0.70822(17); ν₃ + 2ν₅(Σ⁺), 0.80808(25); ν₃ + ν₄ + ν₅(Σ⁺ or Σ^?), 0.73329(17). The band origins were determined (in cm^?1); ν₃, 1045.9242(8); ν₃ + ν₅ ? ν₅, 1049.6441(8); ν₃ + ν₄ ? ν₄, 1047.8700(8); ν₃ + 2ν₅ ? 2ν₅(Σ⁺-Σ⁺), 1053.0374(8); ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅(Σ⁺?Σ⁺ or Σ^??Σ^?), 1051.5040(8).     

Precision infrared spectroscopy in CF379Br by means of infrared-microwave double resonance

From the observation of double resonance effects on the microwave spectrum two coincidences between 9.4 μm CO₂ laser lines and infrared transitions of the ν₆ → (ν₆ + ν₁) band of CF₃⁷⁹Br have been determined: R(30) laser line coincident with ^qR₂(7), F = 17/2→17/2 transition, R(28) laser line coincident with all four ΔF = 0 hyperfine components of the ^qQ₈(13) transition. In both cases other infrared transitions lay within the tuning range of the laser. The frequencies of these two laser lines allowed calculations of the band center frequency ν₀ = 1083.530 ± 0.001cm^?1 and α_A = 11.93 ± 0.3MHz, for the ν₆ → (ν₆ + ν₁) band.α_B constants were determined for the vibrational states v₆, (v₆ + v₁), v₁, and v₃.     

High resolution infrared spectroscopic studies of ethylene-1,1-D2

Rotational assignments in the ν₆ + ν₉ type-A band and the ν₉, ν₆ + ν₁₁, and ν₁ + ν₆ type-B bands of ethylene-1,1-D₂, recorded at a resolution of ～0.03 cm^?1, enable the ground state rotational constants to be determined much more accurately than previously. A significant change in the A₀ constant is noted. All upper states suffer perturbations to their rotational structures. Analyses, excluding the areas of perturbation, still enable the excited state constants to be determined with considerable precision.     

Infrared diode-laser spectrum of the CH3CN ν2 band: Analysis of local resonances with ν6±1 + 2ν8±2, ν4 + ν7±1 + ν8±1, ν4 + ν6±1, ν4 + ν7±1, and 2ν70 + ν8±1 states

Fifty-one sections of infrared diode-laser spectra of acetonitrile have been measured in the region from 2283.5 to 2235.7 cm^?1. About 450 transitions belonging to the ν₂ band have been assigned for K ≦ 7 and J ≦ 44. Anomalies found in the rotational structure have been proven to be due to five local resonances. Observed transition frequencies have been fitted by a least-squares method to a model which includes Fermi-type resonances (Δk = 0, Δ? = ± 3n) with ν₆^±1 + 2ν₈^±2 and ν₄ + ν₇^±1 + ν₈^±1 states, x, y-type Coriolis resonances (Δk = ±1, Δ? = ?3n ± 1) with ν₄ + ν₆^±1 and ν₄ + ν₇^±1 + ν₈^±1 states, and a centrifugal-distortion-type resonance (Δk = ±2, Δ? = ?3n ± 2) with a 2ν₇⁰ + ν₈^±1 state. The 11 × 11 dimensional energy matrix has been diagonalized in order to obtain the perturbed energy levels. The standard deviation for the fit is 1.075 × 10^?3 cm^?1. The molecular constants determined are also listed.     

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: The vibrational dependence of the ν7 bending potential function

Data on the vibrational energy levels and rotational constants of carbon suboxide for the low-wavenumber bending mode ν₇ are reviewed, in the ground-state manifold, and in the ν₂-, ν₃-, ν₄-, and ν₂ + ν₄-state manifolds. Following the procedure developed by Duckett, Mills, and Robiette [J. Mol. Spectrosc.63, 249 (1976)] the data have been inverted to give the effective bending potential in ν₇ for each of these five states. Values are obtained for various other parameters in the effective vibration-rotation Hamiltonian. The potential and rotational constants in ν₂ + ν₄ are given to a close approximation by linear extrapolation from the ground state through the ν₂ and ν₄ states.     

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.     

Analysis of the ν9ν10 band system of allene

The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm^?1) on a Fourier transform instrument in the region 730 to 1170 cm^?1 containing the perpendicular bands, ν₉ and ν₁₀. A total of 21 subbands with KΔK ranging from ?6 to +14 have been assigned in the ν₉ band, and 26 subbands with KΔK = ?10 to +15 have been assigned in the ν₁₀ band. The bands are affected by a combination of a J_z-Coriolis and a quartic anharmonic interaction between their upper states ν₉ and ν₁₀. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν₉ and ν₁₀ upper states. A set of spectroscopic constants for the ν₉ and ν₁₀ states and for some of the perturbing states is reported.     

The vibrational spectrum of thiazole between 600 and 1400 cm revisited: A combined high-resolution infrared and theoretical study

The Fourier transform infrared gas-phase spectrum of thiazole, C₃H₃NS, has been recorded in the 600-1400 cm⁻¹ wavenumber region with a resolution around 0.0030 cm⁻¹. Nine fundamental bands (ν₅(A′) to ν₁₁(A′), ν₁₅(A″), and ν₁₆(A″)) are analysed employing the Watson model. Ground-state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. A detailed analysis of perturbations identified in the ν₁₁(A′) band at 866.5 cm⁻¹ enables a definitive location of the very weak ν₁₀(A′) and ν₁₄(A″) bands at 879.3 and 888.7 cm⁻¹, respectively. The three levels are analysed simultaneously by a model including Coriolis resonance using an ab initio predicted first order c-Coriolis coupling constant; second and higher order Coriolis parameters are determined. Qualitative explanations in terms of Coriolis resonances are given for a number of crossings observed in ν₅(A′), ν₆(A′), and ν₇(A′) at 1383.7, 1325.8, and 1240.5 cm⁻¹, respectively. The rotational constants, anharmonic frequencies, and vibration-rotation constants (alphas, ) calculated by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, have been compared with the present experimental data. The rotation constant differences for each vibrational state, from the ground state values, are closer to experiment from the TZ2P calculations relative to those using cc-pVTZ. The values for Δ_J, Δ_JK, Δ_K, δ_J, and δ_K are close to experiment with both basis sets.     

The infrared spectrum of carbon suboxide in the ν6 fundamental region: Experimental observation and semirigid bender analysis

The infrared spectrum of carbon suboxide, C₃O₂, was measured at high resolution in the region from 500 to 600 cm⁻¹. The spectrum was recorded with a Bomem interferometer at a resolution of about 0.004 cm⁻¹; after deconvolution a resolution of about 0.002 cm⁻¹ was attained. Seven bands were identified and assigned to rovibrational transitions of ¹²C₃¹⁶O₂. These consist of the ν₆ fundamental band and some of the hot bands associated with the ν₇, 2ν₇, and 3ν₇ states. The data obtained on the ν₆ + nν₇ states were used as input for a semirigid bender fit yielding the effective CCC bending potential energy function in the ν₆ state together with a number of related parameters. From the results of the present work together with the results of previous semirigid bender fits it was found that C₃O₂ is bent at equilibrium with an equilibrium CCC bond angle of 156° and a barrier to linearity of 28 cm⁻¹.     

The microwave spectra and vibration-rotation interaction constants for CD3I in the excited vibrational states

The microwave spectra in the J = 1 → 3 region for CD₃I has been observed and six excited vibrational states assigned. The vibration rotation interaction constants, α^B and nuclear quadrupole coupling constants, eQq, have been determined for the states: ν₂, ν₃, ν₅, ν₆, 2ν₃, and ν₃ + ν₆. For the degenerate vibrational states, the l type doubling constants, q_t were determined.     

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).     

Equilibrium structure and anharmonic potential function of phosgene: Diode laser spectra of the ν1 and ν5 bands

The vibration-rotation spectra of the ν₁ and ν₅ bands of phosgene (³⁵Cl₂CO) were measured and analyzed with the aid of Stark modulation spectra for assignment of complicated spectral features. The rotational constants for the ν₁ state were determined to be A₁ = 7885.65(17), B₁ = 3470.25(9), and C₁ = 2406.85(9) MHz. They were used with the ones for the ν₂ ～ ν₆ states reported previously for derivation of the equilibrium rotational constants of ³⁵Cl₂CO: A_e = 7950.35(22), B_e = 3490.22(11), and C_e = 2425.44(22) MHz.     

Water-vapor absorption spectrum in the 0.59-μm region

The paper gives the results of investigation of the water-vapor absorption spectrum in the range of 586.9–596.6 nm. In the given range, 282 water-vapor absorption lines were recorded and were identified as belonging to the bands 4ν₁ + ν₃, 3ν₁ + 2ν₂ + ν₃, 3ν₁ + 2ν₃. Theoretical justification of the technique for interpreting the observed spectrum was made. The values of more vibration-rotation levels of energy were determined: for state (401) up to J = 10, for state (321) up to J = 10, and for state (302) up to J = 8. The rotational and centrifugal constants of the reduced Watson's Hamiltonian for the vibrational states (401), (321), (302), and (222) and constants of Fermi resonance (401)-(321), (302)-(222), and Coriolis resonance between the states (401), (321), and (302), (222) 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.