Millimeter-Wave Spectroscopy of ClBS: An Improved Evaluation of the Equilibrium Structure of Chlorothioborine

The rotational spectrum of the unstable ClBS molecule has been investigated in the millimeter-wave region, from 80 to 195 GHz. A high-temperature reaction between crystalline boron and disulfur dichloride vapor was used to produce the molecule in a flow pyrolysis system. Eight different isotopic species were studied measuring lines in the ground and excited vibrational states 01¹0 (ClBS bend), 10⁰0 (ClB stretch), 02⁰0, 02²0, and 00⁰1 (BS stretch). The analysis of the spectra has been performed taking simultaneously into account both the Fermi resonance between the 10⁰0 and 02⁰0 states, and l-type resonance effects in the v₂=2 vibrational state. This procedure allowed us to calculate directly deperturbed rotational constants, from which the equilibrium rotational constant of seven isotopic variants could be accurately determined yielding a much improved evaluation of the equilibrium structure of chlorothioborine: r_e(ClB)=1.6806±0.0001 Å and r_e(BS)=1.6049±0.0001 Å. The equilibrium structures of ClBS and of the related molecules HBS, FBS, HCP, FCP, and ClCP have been also theo-retically evaluated by high-level CCSD(T) calculations performed using cc-pVTZ, cc-pVQZ, and cc-pV5Z basis sets. The different trends respectively observed for the BS and CP bond lengths in the XBS and XCP triatomic molecules are discussed.     

The microwave spectrum of silyl isocyanate, SiH3NCO: Spectra of isotopically substituted species and correction of the rs structure

Microwave spectra have been measured for 10 isotopic species of silyl isocyanate, SiH₃NCO, in the ground vibrational state, and in several excited states of the lowest frequency bending vibration, ν₁₀. This vibration is highly anharmonic, with a potential hump of 31.5 cm⁻¹ at the linear configuration, and its effects have been removed from the rotational constants to produce effective ground-state rotational constants B₀^* for each isotopic species. These B₀^* constants have been used to determine the structural parameters, which are now in good agreement with earlier electron diffraction values. Excellent predictions have been made of the centrifugal distortion constants for different isotopic species and vibrational states, as well as of the l-type doubling constants of the various isotopic species.     

Millimeter and submillimeter-wave spectroscopy of silicon difluoride

The rotational spectra of ²⁸SiF₂, ²⁹SiF₂, and ³⁰SiF₂ in their ground vibrational states, as well as those of ²⁸SiF₂ in the v₁ = 1, v₂ = 1, v₃ = 1, and v₂ = 2 excited states have been studied in selected frequency regions between 80 and 700 GHz. Transitions involving a large range of quantum numbers have been observed, so that precise rotational and quartic centrifugal distortion constants could be determined for each of the spectra investigated. In addition, the complete set of sextic distortion constants was also obtained for the most abundant isotopomer in its ground vibrational state. The quadratic and cubic force constants of silicon difluoride have been refined by a least-squares procedure using a larger and more precise set of data.     

Rotational Spectroscopy of HBS: The Quadrupole Coupling Constant of S in Thioborine

The unstable HBS molecule has been produced in the gas phase by a high-temperature reaction between crystalline boron and hydrogen sulfide. Ground state rotational spectra have been observed in the millimeter-wave region, from 75 to 460 GHz, for the previously unobserved H¹¹B³³S and H¹⁰B³³S isotopic species. The analysis of the hyperfine structure produced by the ^10/11B and ³³S nuclear spins in the low-J rotational transitions has yielded the first evaluation of the quadrupole coupling constant of 33S in the thioborine molecule, which was 6.361(15) MHz in H¹¹B³³S and 6.329(17) MHz in H¹⁰B³³S. In addition, further measurements have been performed for the most abundant isotopomers H^10/11B^32/34S, for which improved values of rotational, centrifugal, and hyperfine structure constants have been determined.     

Spectroscopic constants of the ground and lower vibrational states of CH2BrF: A combined high resolution infrared and microwave study

The enriched ⁸¹Br isotopic species of bromofluoromethane has been investigated in the infrared and microwave regions. The rovibrational spectrum of the ν₅ fundamental has been studied by high resolution FTIR spectroscopy, while the rotational spectra of the ground and v₆ = 1 states have been observed by means of microwave spectroscopy. More than 2700 transitions have been assigned in the ν₅ band and the analysis of the rovibrational structure reveals a first-order c-type Coriolis resonance with the v₆ = 2 state. The present study improves the ground state constants available in the literature and enables the determination of further centrifugal distortion parameters together with the full bromine quadrupole coupling tensor. A set of spectroscopic parameters up to the sextic distortion terms for the vibrational excited states has been accurately evaluated for the first time.     

Sub-millimeter spectroscopy of BaS (XΣ)

The pure rotational spectrum of BaS (X¹Σ⁺) has been recorded in the frequency range 355-396 GHz using direct absorption methods. Data were recorded for six isotopomers: ¹³⁸Ba³²S, ¹³⁷Ba³²S, ¹³⁶B³²S, ¹³⁵Ba³²S, ¹³⁴Ba³²S, and ¹³⁸Ba³⁴S, in vibrational states ranging from v = 0 to v = 6. This work is an extension of past microwave and millimeter studies. Revised spectroscopic constants have been established for the six species. The dissociation energy for ¹³⁸Ba³²S is estimated to be 42 392 cm⁻¹.     

High resolution infrared spectrum of 13CS2 between 250 and 430 cm−1

The high resolution infrared spectrum of ¹³CS₂ between 250 and 430 cm^?1 has been studied with a Fourier transform spectrometer at a resolution of about 0.010 cm^?1. The following bands are analyzed: the bending fundamental 01¹0←00⁰0 of ¹³C³²S₂ and the associated “hot” bands 02²0←01¹0, 02⁰0←01¹0, 03³0←02²0, 03¹0←02⁰0, 03¹0←02²0, 11¹0←10⁰0, the difference band 10⁰0←01¹0 of ¹³C³²S₂, and the bending fundamental 01¹0←00⁰0 of ³²S¹³C³⁴S. The polynomial fits were used in the analyses. The rotational constants B and D together with the vibrational term values have been derived for the states involved. The l-type doubling constant q has been obtained for the Π-states 01¹0, 11¹0, and 03¹0 of ¹³C³²S₂.     

New measurements of the microwave spectrum of formamide

New measurements of the microwave spectrum of formamide have been obtained in the frequency range from 49 to 340 GHz using the microwave spectrometer at the Institute of Radio Astronomy of NASU, Kharkov, Ukraine. An analysis of the rotational spectra of the ground, v₁₂, v₉, v₁₁ and 2v₁₂ excited vibrational states of the main isotopic species as well as of the ground states of the ¹³C, ¹⁵N and ¹⁸O substituted species has been carried out using SPFIT/SPCAT programs. The analysis of a strong Coriolis interaction coupling between v₉, v₁₁ and 2v₁₂ vibrational states of formamide has been also fulfilled as well as the analysis of the quadrupole hyperfine structure of the observed transitions. For the first time the quadrupole coupling parameters for the excited vibrational states and for the ¹⁸O substituted species of formamide were determined.     

Submillimeter-wave spectroscopy of HCO in the excited vibrational states

The pure rotational transitions of HCO⁺ in excited vibrational states located below 5000 cm⁻¹ over the ground state have been investigated with a high-sensitivity frequency/magnetic field double modulation submillimeter-wave spectrometer in the frequency range of 280-810 GHz. The ions were generated in an extended negative glow discharge through a gas mixture of a few millitorrs of H₂ and CO and 12 mTorr of Ar buffer gas. Throughout the experiments, the cell was maintained at liquid nitrogen temperature. In the present study, we have determined accurate molecular constants for the excited vibrational states. Our analysis suggests that there may be a higher order Coriolis interaction between the (0 3 1) and (1 2 0) states. In previous investigations, the Stark effect caused by the electric field present in the discharge plasma was cited as a reason for non-observations of low-J lines in the (02²0) and for the systematic shifts observed for low-J lines in the (01¹0), (02²0), (03¹0), and (04²0) states of HCO⁺ as well as DCO⁺. In the present investigation, some low-J lines in the (02²0) and (04²0) states have been observed in emission. Furthermore, J = 8-7, J = 9-8 lines in (03^1e1) were detected in emission. This finding indicates that missing low-J lines for the Δ sublevel obtained in the past is not due to the Stark effect but due to small population differences in those levels.     

Laser spectroscopy of the B[17.7]8-X8 and C[19.3]9-X8 transitions of holmium monochloride

Several new transitions of holmium monochloride (HoCl) have been studied at high resolution using laser excitation spectroscopy. Two main transitions, B[17.7]8-X8 and C[19.3]9-X8 have been observed and five bands, 0-0, 0-1, 1-0, 1-1, and 2-1 of the B-X transition and three bands, 0-0, 0-1, and 0-3 of the C-X transition have been obtained at high resolution and rotationally analyzed. Among several low lying states observed in dispersed fluorescence was a strong transition from the C state to a state ∼2140 cm⁻¹ above the ground state. Excitation spectra of this transition have shown that there are apparently two states, ∼6 cm⁻¹ apart. Comparison with ligand field theory calculations are consistent with assigning these states to the excited low lying Ho⁺(4f¹¹6s)Cl⁻ configuration. Several other low lying electronic states have been observed in dispersed fluorescence spectra. Although their assignments could not be established, their energies suggest that they are from the Ho⁺(4f¹⁰6s²)Cl⁻ or Ho⁺(4f¹¹6s)Cl⁻ configurations. Rotational constants have been obtained for the B[17.7]8 and C[19.3]9 states and have been used to speculate on the possible electron configurations for these states.     

Franck-Condon factors and r-centroids of B-X, C-X and C-A band systems of AlO molecule

Using the high resolution Fourier transform spectrometer the B²Σ⁺-X²Σ⁺ band system of AlO molecule has been recorded. The rotational structure of eighteen bands belonging to B²Σ⁺-X²Σ⁺ transition of AlO have been analyzed which led to accurate rotational and vibrational constants of ground and excited states. A few bands, viz. (2, 1), (3, 2), (4, 3), (2, 3), (3, 4), (4, 5), and (5, 6) were analyzed for the first time. Using these constants, the Franck-Condon factors and r-centroids were computed for the bands of B-X, C-X and C-A band systems for the v′ = 0-8; v″ = 0-8 matrix using the method developed by Jarmain and Nicholls. The F-C factors and r-centroids obey the established relationships.     

Rotational spectrum of the v11 = 1 and v14 = 1 vibrational states of CH3CCCCH

The pure rotational spectra of the v₁₁ = 1 and v₁₄ = 1 vibrational states of the main isotopic species of methyldiacetylene have been recorded and assigned in the 80-400 GHz frequency range, spanning the quantum numbers 19 ? J ? 95 and 0 ? K ? 15. The present study allows us to provide accurate rotational, centrifugal distortion and vibration-rotation interaction constants. The experimental investigation has been strongly supported by quantum-chemical computations at the second-order Møller-Plesset theory (MP2) in conjunction with a triple-zeta quality basis set.     

Submillimeter microwave spectrum and spectroscopic constants of the OCS molecule: Isotopic species 16O12C33S and 18O12C32S

Microwave spectra of ¹⁶O¹²C³³S and ¹⁸O¹²C³²S in their natural isotopic abundances were investigated in the range 280–510 GHz. The effective rotational and centrifugal constants have been determined for all observed vibrational states. An analysis of the rotational spectrum taking account of l- and Fermi-resonances has been performed within each isotopic species.     

Comprehensive analysis of the FASSST rotational spectrum of S(CN)2

Results are reported of a comprehensive investigation of an almost continuous rotational spectrum of S(CN)₂ recorded over the frequency region 110-374 GHz by means of the FASSST spectroscopic technique. The spectrum was analysed in detail and over 22 000 transitions were assigned in total. Precise, octic order spectroscopic constants in the asymmetric rotor Hamiltonian have been determined for the ground state and 12 different vibrationally excited states of the parent isotopologue, including first excited states of five different normal modes. Three states near 370 cm⁻¹ and four states near 490 cm⁻¹ above the ground state were found to be mutually interacting and were successfully analysed in terms of a triad and a tetrad of coupled states, respectively. Rotational transitions in the ³⁴S, ¹³C, and ¹⁵N isotopologues of S(CN)₂ have also been assigned and fitted, and newly determined rotational constants were used to derive the geometry of the molecule. The complex multistate analysis of the spectrum was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra.     

The analysis of combination and overtone states of BF3 from 1650 to 4600 cm

High-resolution (0.0015-0.0035 cm⁻¹) infrared spectra of isotopically enriched ¹¹BF₃ have been examined in detail. The analysis of the combination and overtone states within the region of study, from 1650 to 4600 cm⁻¹, led to the assignment of over 25,000 transitions. The major perturbations were due to the Fermi resonances between states possessing one quantum of v₃ and three quanta of v₄. With corrections through the quadratic rotational terms, the equilibrium B_e and C_e values have been determined; 0.3462679(7) cm⁻¹ and 0.1731151(6) cm⁻¹, respectively. An improved set of equilibrium rotational constants for ¹⁰BF₃, consistent with this analysis of ¹¹BF₃ are also given. The averaged equilibrium values for both isotopomers lead to a B-F bond distance of r_e = 130.704 ± 0.005 pm. All of the quadratic anharmonic constants, with the exception of x³³ were independently determined from experiment. For the first time for BF₃, a normal force field analysis was performed that utilized the experimentally determined, fundamental harmonic vibrational frequencies.     

Submillimeter-wave spectroscopy of HN2 and DN2 in the excited vibrational states

The pure rotational transitions of HN₂⁺ and DN₂⁺ in the first excited vibrational states for all the fundamental vibrational modes have been observed in the range of 300-750 GHz. The molecular constants determined are much more accurate compared with those obtained from the infrared spectroscopy. The equilibrium rotational constants, B_e = 46832.45 (71) MHz for HN₂⁺ and B_e = 38708.38 (58) MHz for DN₂⁺, have been determined by correcting for the higher-order vibration-rotation interaction effects, γ_ij, obtained by an infrared investigation. The equilibrium bond lengths are derived from these equilibrium rotational constants: r_e(H-N) = 1.03460 (14) Å and r_e (N-N) = 1.092698 (26) Å.     

Rotational spectrum of trans-trans diethyl ether in the ground and three excited vibrational states

We report the results of a comprehensive reinvestigation of the rotational spectrum of diethyl ether based on broadband millimetre-wave spectra recently recorded at The Ohio State University and in Warsaw, covering the frequency region 108-366 GHz. The data set for the ground vibrational state of trans-trans diethyl ether has been extended to over 2000 lines and improved spectroscopic constants have been determined. Rotational spectra in the first excited vibrational states of the three lowest vibrational modes of trans-trans-diethyl ether, ν₂₀, ν₃₉, and ν₁₂ have been assigned. The v₂₀ = 1 and v₃₉ = 1 states are near 100 cm⁻¹ in vibrational term value and are coupled by a strong c-axis Coriolis interaction, which gives rise to many spectacular manifestations in the rotational spectrum. All of these effects have been successfully fitted for a dataset comprising over 3000 transitions, leading to precise determination of the energy difference between these states, (ΔE/hc)=10.400222(5) cm⁻¹. A newly developed software package for assignment and analysis of broadband spectra is described and made available.     

Millimeterwave spectrum of DC discharge produced ICN in excited vibrational states

An indigenously built 50 kHz source-modulated millimeter-wave spectrometer was used to produce cyanogen iodide (ICN) in the excited vibrational states (01¹0), (03³0), (10⁰0), (20⁰0) and (02⁰0) and record their corresponding rotational spectra. The analysis of the recorded spectra was carried out in the frequency range of 57.0–98.0 GHz. ICN was produced using a DC glow discharge through a mixture of methyl iodide (CH₃I) and benzyl cyanide (C₆H₅CH₂CN) vapor at low pressure. ¹²⁷I nuclear quadrupole hyperfine structure and the l-type doublet spectra of (01¹0) state have been resolved. The observed and assigned rotational transition frequencies were used in a least-square fit to determine more accurate values of molecular constants. The agreement between the derived parameters and those reported earlier clearly indicate that the reported spectral lines belong to ICN in the excited vibrational states. It also indicates that ICN could be produced in selective excited vibrational states by DC glow discharge technique.     

The Pure Rotational Spectrum, Geometry, and Hyperfine Constants of Hafnium Monosulfide, HfS

The pure rotational spectra of seven isotopomers of hafnium monosulfide have been measured for several vibrational states. For the most abundant isotopomer, ¹⁸⁰Hf³²S, the J=1 - 0, J=2 - 1, and J=3 - 2 transitions were recorded up to the sixth vibrationally excited state. The constants Y₀₁, Y₀₂, Y₁₁, Y₂₁, and Y₃₁ were determined via a multi-isotopomer fit to a Dunham-type expression. In the process of fitting the data it was necessary to include Born-Oppenheimer breakdown correction terms. The equilibrium internuclear distance has been evaluated. For both the ¹⁷⁷Hf³²S and ¹⁷⁹Hf³²S isotopomers, nuclear hyperfine structure due to the hafnium nucleus was observed and notably large Hf nuclear quadrupole coupling constants, eQq, were determined.     

Experimental and theoretical study of the electronic states and spectra of PbLi

Gas phase emission spectra of the hitherto unknown free radical PbLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which lead vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Five electronic transitions have been found in the wavenumber range 3800-10 000 cm⁻¹. Bands from two excited states to the ground state were measured at high spectral resolution such that rotational analyses could be performed and accurate molecular parameters derived. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of PbLi and also electric dipole transition moments connecting them. As in the lighter molecules of this group, CLi and SiLi, the ground state of PbLi is found to be 3/2) with a spin splitting of about 2000 cm⁻¹. The first excited state is (A 1/2), and two observed band systems are assigned to the transitions A→X₁ and A→X₂. Two more excited states, (B 3/2) and C 1/2, are identified from the observed spectra with the help of the computed data, and their spectroscopic constants are determined. In contrast to PbH and PbF, the ab initio results indicate a very complicated low-energy electronic structure for the PbLi radical, with 19 bound electronic states calculated to lie below 3 eV.