Ground State Combination Differences Research Articles

The High-Resolution Infrared Spectrum of FNO2between 500 and 900 cm−1: The ν5, ν3, ν6, ν2Coriolis Interacting Tetrad

The gas-phase IR spectra of the ν5, ν3, ν6, and ν2bands of FNO2have been studied at resolutions ranging from 0.0023 to 0.0050 cm−1. These bands form an isolated tetrad which is coupled bya-,b-, andc-Coriolis resonances. Thec-Coriolis interaction between ν3and ν5is particularly strong. From a ground state combination difference analysis the following ground state rotational constants have been obtained:A= 0.440348960(17) cm−1,B= 0.381803994(17) cm−1, andC= 0.204107899(13) cm−1. A simultaneous upper state analysis with a four level model based on the Watson asymmetric top Hamiltonian and taking into account Coriolis interactions has been performed. A set of spectroscopic parameters for the ν5, ν3, ν6, and ν2levels has been obtained.

Strong and Isotope Selective Effects of the ΔK= ±3 Interaction in the Ground State and in the ν5Infrared Bands of Four Isotopomers of FClO3

The infrared spectra of monoisotopic samples of the35/37Cl and16/18O isotopomers of FClO3have been recorded in the region of the ν5fundamental with a resolution of ca. 3 × 10−3cm−1. Several thousand lines have been assigned in each species and ground state molecular parameters have been determined or improved through the use of ground state combination differences. It was shown that an agreement between the ground state parameters of the four isotopomers requires a ΔK= ±3 interaction with an off-diagonal ϵ term introduced. The main perturbation in thev5= 1 state is due to a ΔK= ±3 interaction which has very strong effects because levels differing by 3 units inKcan be unusually close. For F35Cl18O3and F37Cl18O3, the effects are largest forkl= −23 and −26 and give rise to “perturbation-allowed transitions.” For F35Cl16O3and F37Cl16O3, thekl= −5 and −8 levels are closest and no perturbation-allowed transition could be assigned. Two different interaction terms, called ϵ andd, can be defined for such interactions in a degenerate vibrational state. For the first time, they have been both determined significantly and simultaneously for all four isotopomers. They adopt values almost independent of35Cl/37Cl substitution and consistent in the16O/18O substitution, in spite of very different resonance effects. The axial rotational constantsA0have also been determined with high accuracy.

The Si–H Stretching Fundamentals of H328SiD

The ν1(A1) and ν4(E) Si–H stretching fundamentals of H3SiD have been recorded at an effective resolution of 0.006 cm−1between 2050 and 2300 cm−1. A total of about 2500 rovibrational transitions of the H328SiD isotopomer have been assigned withJ′ up to 27 andK′ up to 22. A large number of “perturbation allowed” Δk= ±3 transitions have been identified in both the ν1and ν4bands. The assigned transitions have been analyzed using two different theoretical models, which took into account several rovibrational interactions between and within thev1= 1 andv4= 1 states, yielding a standard deviation of each fit of ca. 0.0004 cm−1, which may be compared with the experimental precision (ca. 0.0001 cm−1). Improved ground state parameters have also been obtained by means of ground state combination differences.

Observation of Δ|k − l| = 3 Transitions in the ν3Band of H3O+

Although the vibration–rotation spectrum of H3O+has been studied extensively, there has been no experimental information on the value of theCrotational constant because of the absence of any observed Δ|k − l| ≠ 0 forbidden transitions. However, as pointed out by Verhoeveet al.in their far-infrared spectroscopic work [P. Verhoeve, M. Versluis, J. J. Ter Meulen, W. L. Meerts, and A. Dynamus,Chem. Phys. Lett.161,195–201 (1989)], a near degeneracy exists between some (J, 0)+and (J, 3)−ground state rotation–inversion levels, which causes sizable shifts in these levels due to off-diagonal centrifugal distortion. These shifts were observed in the ground state combination differences of the ν3fundamental transitions. We have observed 11 forbidden Δ|k − l| = 3 transitions to the ν3band induced by the mixing in the ground state and involving theJ= 7, 9, and 11 levels, and determined the energy difference between differentKlevels, theCrotational constant, and the off-diagonal centrifugal distortion mixing coefficient.

Combined high resolution infrared and microwave study of bromochlorofluoromethane

We report a detailed spectroscopic investigation of the chiral molecule bromochlorofluoromethane (CHBrClF) with rotational resolution using a pulsed nozzle beam Fourier transform microwave (FTMW) and a waveguide FTMW spectrometer as well as a supersonic jet interferometric Fourier transform infrared (FTIR) and infrared diode laser spectrometer. The rotational spectrum of CHBrClF has been measured between 8 and 18 GHz. The quadrupole hyperfine components have been fully resolved for the assigned rotational transitions with J⩽18. Three ground state rotational constants, five centrifugal distortion constants, and all five independent elements of the bromine and chlorine quadrupole coupling tensors have been determined for each of the four isotopomers CH79Br35CIF, CH81Br35CIF, CH79Br37CIF, and CH81Br37CIF from about 500 measured transition frequencies of the hyperfine components. The quadrupole coupling tensor has been transformed to its principal axes. The determinable sign combinations of the off-diagonal elements of the coupling tensor have been evaluated. Rotational transitions involving high J were measured by FTIR spectroscopy between 15 and 40 cm−1 (450–1200 GHz) using a light pipe cell, providing an estimate of the permanent dipole moment |μ|=(1.5±0.3) D from intensities. In the midinfrared, we have fully analyzed the rovibrational line structure of supersonic jet spectra of the CF-stretching fundamental ν4, giving band centers for the isotopomers CH79Br35CIF [ν̃ 40=1077.178 43(4) cm−1], CH81Br35CIF [ν̃=1077.133 06(4) cm−1], CH79Br37CIF [ν̃ 40=1076.7914(4) cm−1], and CH81Br37CIF [ν̃ 40=1076.730 26(5) cm−1]. A combined analysis of about 20 microwave frequencies, more than 100 infrared ground state combination differences, and about 70 infrared transition frequencies for each of the35Cl isotopomers finally provide accurate ground and excited state rotational parameters as well as structural parameters, which may be compared to ab initio calculations. The results are discussed in relation to the molecular structure as well as coincidences of ν4 absorptions with CO2 laser lines in view of CO2–laser pumping and possible spectroscopic studies of this chiral molecule at ultrahigh resolution.

A Long Path Cell for the Fourier Spectrometer Bruker IFS 120 HR: Application to the Weak ν1+ ν2and 3ν2Bands of Carbon Disulfide

The construction and properties of a White cell connected to a Bruker IFS 120 HR spectrometer are described. The maximum path length attainable is about 200 m. The cell and its use in accurate measurements where the calibration is performed with the aid of CO2laser lines in absorption has been tested with the weak bands ν1+ ν2and 3ν2of CS2. From the ground state combination differences of these bands, new, more accurate rotational constants were derived:B0= 0.109126043(50) cm−1andD0= 1.17678(31) × 10−8cm−1. The bands were fitted with a standard deviation of 4.8 × 10−5cm−1by using a model, where thel-type and Fermi resonances were included. The intensities in the bands were strikingly perturbed. These anomalies were explained and simulated with the Herman–Wallis effect.

Accurate Determination of the Ground State Constants of H3SiF IncludingA0andD0Kfrom the ν6, 2ν±26− ν±16, and 2ν∓26Rovibrational Bands

In order to determine ground state parameters, high-resolution FTIR spectra of H3SiF have been studied in the ν3/ν6(620–960 cm−1) and 2ν6/ν3+ ν6/2ν3(1300–1800 cm−1) regions. The fundamentals ν3and ν6, the combination band ν3+ ν6, and the overtones 2ν06, 2ν∓26, and 2ν3have been assigned. Using “ordinary” ground state combination differences obtained from the ν3and ν6bands, improved ground state parametersB0,D0J,D0JK,H0J,H0JK, andH0KJwere determined for the main isotopomer H328SiF. The hot bands 2ν±26− ν±16, 2ν06− ν∓16, and (ν3+ ν±16) − ν±16of H328SiF have been assigned. The ν6, 2ν∓26, and 2ν±26− ν±16bands were used for the first experimental determination of the ground state constantsA0andD0K, whereas (ν3+ ν±16) − ν±16and 2ν06− ν∓16served for calibration purposes. Ground state differences Δ(K,J) =E0(K,J) −E0(K− 3,J) could be calculated forK= 2 to 12. By a least-squares fit of 523 such differences, we obtained the following results (in cm−1):A0= (2.8378883 ± 0.0000046) andD0K= (1.9236 ± 0.0020) × 10>−5.

High-Resolution Infrared Study oftrans-Monodeutero-diimide, HNND

Infrared spectra oftrans-monodeutero-diimide, HNND, have been recorded between 760 and 3250 cm−1at a resolution of ca. 0.005–0.007 cm−1, from which the fundamental bands ν1, ν4, ν5, and ν6of this isotope have been studied. A detailed analysis of thea,b-Coriolis interacting band system ν5, ν6near 1100 cm−1is presented. The ν4band at 1475 cm−1has been analyzed by a model includingc-Coriolis and ΔKa= ±2 vibrational resonance with the close lying ν3band at 1538 cm−1. Only 18 transitions in ν3which obtain their intensity through interaction with the ν4band have been assigned. Together with the observed perturbation effects in ν4they provide valuable information for the ν3level, too. In the ν1band around 3110 cm−1numerous local crossings due to vibrational andc-Coriolis interactions with the unobserved binary combinations 2ν3, ν3+ ν4, and 2ν4have been identified. The present analyses yield a number of spectroscopic constants for the ν1, ν3, ν4, ν5, and ν6levels and various interaction constants. From a simultaneous ground state combination difference analysis of the four observed bands the following ground state rotational constants are obtained:A0= 7.384213(4) cm−1,B0= 1.1959457(6) cm−1, andC0= 1.0255827(6) cm−1.

The Rotational Spectrum of H2Te

In the present work, we study the spectrum of the H2Te molecule in the submillimeter-wave and far infrared region. An important aim of this investigation is the further experimental characterization of the anomalous “four-fold cluster effect” exhibited by the rotational energy levels in the vibrational ground state of H2Te. The spectrum in the region 90–472 GHz was measured with a source-modulated millimeter-wave spectrometer and that between 600 and 1600 GHz with a far-infrared sideband spectrometer. The far infrared spectrum from 30 to 360 cm−1was measured with a Bruker IFS 120 HR interferometer attached to a 3 m long cell. We have assigned 224 submillimeter-wave lines and 1695 FIR lines. These observed data were supplemented by a large number of ground state combination differences derived from rotation–vibration bands of H2Te, and the resulting large data set was analyzed by means of a modified Watson Hamiltonian. Accurate sets of rotational and centrifugal distortion constants for all eight tellurium isotopomers were obtained.

High-Resolution Infrared Study of the ν4, ν5, and ν6Bands oftrans-Dideutero-di-imide, DNND

The gas-phase IR spectra of thea,b-Coriolis interacting band system ν4,ν6around 950 cm−1and the ν5band around 2300 cm−1of N2D2have been recorded with a resolution of ca. 0.005 and 0.007 cm−1, respectively. In the ν5and ν6bands botha- andb-type components are observed. In ν4thec- and a parallel-type component which obtains its intensity from the stronga-Coriolis resonance with ν6are observed. In addition, ΔKa= ±2 band components which are due to strongb-Coriolis perturbation are observed in both ν4and ν6. From a simultaneous ground state combination difference analysis of all three bands the following ground state constants are obtained:A0= 6.0245856(22) cm−1,B0= 1.08957754(33) cm−1, andC0= 0.91955624(33) cm−1. The upper state energies from the ν4, ν6band system have been analyzed using a dyad model including first and higher ordera- andb-Coriolis interactions between these levels. In the analysis of the ν5band weak higher orderc-type and vibrational type ΔKa= ±2 interactions with the unobserved combination band ν3+ ν6are taken into account. Upper state spectroscopic constants for all three levels and a number of interaction constants have been determined from these analyses.

Combined Analysis of the Rotational and Infrared Spectra of Four Fundamentals, ν2(A1), ν3(A1), ν5(E), and ν6(E), in12CD3F and13CD3F

Submillimeter wave rotational spectra of the vibrational states ν2(A1), ν3(A1), ν5(E), and ν6(E) in12CD3F and13CD3F have been recorded and assigned. The new data with previously published high resolution infrared spectra have been used to determine the excited state rotational parameters. The upper states of the four fundamentals in each isotopic species were treated simultaneously due to strong vibration-rotation interactions. Both ground state combination difference data from the previously published infrared transitions and ground state rotational transitions have been used to determine accurate ground state rotational parameters including the rotational constantA0and the centrifugal distortion constant[formula]The number of observed rotational transitions in the vibrationally excited states is 131 for12CD3F and 109 for13CD3F, respectively.

The ν4Band of Ammonium, NH+4

The ν4band of NH+4was observed with a diode laser spectrometer. The molecular ions were generated in a water-cooled, concentration-modulated, hollow-cathode discharge of hydrogen and ammonia gases. Forty lines were measured and assigned to NH+4. These new data were combined with 56 previously published ν4transitions, and 24 ground state combination differences from the ν3band. The combined data set was fit with a fourth-order spherical rotor Hamiltonian to provide improved molecular parameters for thev4= 1 and ground states.

Ground State Rotational Energies of Arsine

An analysis of the ground state of arsine is performed by using all the line assignments coming from a recent investigation of the vibrational system 2ν2/ν2+ ν4/2ν4/ν1/ν3at 1650–2350 cm−1. A set of 6837 ground state combination differences is used, in combination with all FIR and radio-wave and microwave data (RMW) available in the literature, to refine the ground state parameters. The rotational model takes into account all the nondiagonal contributions in 〈K|K± 3〉 and 〈K|K± 6〉, which are calculated via diagonalization, as well as the hyperfine interactions. The best estimates of the ground state parameters include 12 rotational and 4 quadrupole parameters. The overall rms deviation of the fit is 0.225 MHz for 7142 data fitted. The deviations for IR, FIR, and RMW data separately, are 0.329 × 10−3cm−1, 0.279 × 10−3cm−1, and 0.149 MHz, compared to average experimental uncertainties estimated to 0.5 × 10−3cm−1, 0.2 × 10−3cm−1, and 0.211 MHz for the three kinds of data, respectively. The parameters are compared to previous results and used for a prediction of the ground state energies up toJ= 20, including hyperfine structure. A list including calculated line frequencies and intensities for all the ground state rotational transitions obeying either ΔJ= 1, Δ|K| = 0, ΔF= 0, ± 1, or ΔJ= 0, Δ|K| = 0, ±3, ΔF= 0, ±1, is also produced up toJ= 20.

Ground state constants A 0, D K 0 and H K 0 of 13CH3I from normally allowed infrared absorption bands

The axial ground state constants A 0, D K 0 and H K 0 of 13CH3I were determined by combining lines from three perpendicular bands: the fundamental band v 6, its overtone 2v 6, and the related hot band 2v 6-v 6. Ground state combination differences, where ΔK = 3, were calculated for ten K value pairs from (3,0) to (12,9). As a result, values A 0 = 5·1742629(14) cm-1, D K 0 = 87·857(33) × 10-6 cm-1, and H K 0 = 4·44(21) × 10-9 cm-1 were obtained.

Resonance between the Ground Vibrational State and the Lowest Frequency Bending Mode of Thioketene

Far-infrared and mid-infrared spectra of thioketene have been recorded over the region 200–1250 cm−1and transitions assigned from the ν4, ν5, ν6, and ν9fundamentals and ν5+ ν9← ν9and ν5+ ν6← ν6hot bands. Ground state combination differences from ν4and ν5, together with ν6and ν9transitions, lower state combination differences from the ν5+ ν9← ν9and ν5+ ν6← ν6hot bands, and previous millimeter-wave data, have been included in a combined fit of ν6, ν9, and the ground state. The stronga-axis Coriolis interaction between ν6and ν9has been treated along with thec-axis centrifugal distortion interaction between ν9and the ground state. The magnitudes of these interactions are in agreement with values obtained fromab initiomolecular orbital calculations at the MP2/6-311G** and CCSD/6-311G** levels of theory.

Complete Structure of trans-1,2-Difluoroethylene from the Analysis of High-Resolution Infrared Spectra

For comparison to the structure of the cis isomer with its puzzlingly lower energy, the complete structure of trans-1,2-difluoroethylene, a nonpolar molecule, has been determined. High-resolution infrared spectra have been recorded for three isotopomers, the 13C2, d2, and d1 species. From the analysis of at least two band types for each isotopomer, a Watson-type Hamiltonian has been fit to ground state combination differences. Ground state rotational constants (in cm-1) are A = 1.8247501(32), B = 0.13396608(66), and C = 0.12473595(65) for the 13C2 species, A = 1.2634959(27), B = 0.13403712(61), and C = 0.12110234(59) for the d2 species, and A = 1.5198818(34), B = 0.13429738(50), and C = 0.12331713(54) for the d1 species. From these constants and those previously published for the normal species, substitution coordinates have been found for the carbon and hydrogen atoms and effective coordinates have been found for the fluorine atoms. The resulting parameters are rCH = 1.080 A, rCC = 1.316 A, rCF = 1.352 A...

Millimeter-Wave Spectra,ab InitioCalculations, and Structures of Fluorophosphane and Chlorophosphane

The structures of fluorophosphane, PH2F, and chlorophosphane, PH2Cl, have been calculated ab initio at the SCF, MP2, CCSD, and CCSD(T) levels using a quadruple ζ polarized basis set. Equilibrium and ground state rotational constants as well as centrifugal distortion constants have been predicted for several isotopomers of PH2F and PH2Cl. Theoretical CCSD(T) geometries were also determined for the series of PHnX3-n (X = F, Cl; n = 0−3) molecules using a triple ζ polarized basis set. The millimeter-wave spectra of the short-lived molecules PH2F, PH2Cl, and their perdeuterated species were measured in the frequency range 100−470 GHz. For PH2F and PH2Cl, accurate ground state parameters have been obtained by a combined fit of the millimeter-wave data and the infrared ground state combination differences. The ro, rz, and re structures of PH2F and PH2Cl, as well as PH3, PCl3, and PHF2 have been determined. The experimental results are found in excellent agreement with their ab initio predictions.

Detection of Short-Lived PH 2I by High-Resolution Infrared and Millimeter-Wave Spectroscopy: The Ground, ν 3, ν 4, and ν 6 Excited States

By low-resolution IR spectroscopy the ν 2 and ν 3 fundamental vibrations of the hitherto unknown PH 2I molecule were detected when P 2H 4 was reacted with HI in the gas phase. At room temperature and a pressure of 1-4 mbar the half-life of PH 2I was determined to be ca. 30 sec. High-resolution IR spectra (resolution ca. 6 × 10 −3 cm −1) were recorded in the ν 3 and ν 6 regions near 750 and 340 cm −1. While rotational J, K lines of the near symmetric top molecule were resolved in the ν 3 band, the ν 4 band revealed sharp (although unresolved) J clusters, which were also found for the hot bands 2ν 4-ν 4 and 3ν 4-2ν 4. Millimeter-wave spectra were recorded in the 350 to 460 GHz range, and ground state constants determined by merging Δ K a = 0 pure rotational data with ground state combination differences. For A reduction and I r representation the following constants were determined: A = B z 4.35(5), B = B x 0.104 876(3), and C = B y 0.104 646(3) cm −1. The analysis of the ν 3 band revealed a c-type Coriolis resonance of ν 3, ν 0, 752.525 25(7) cm −1, with ν 6, ν 0 742.684(11) cm −1, and ζ c 3,6 (−)0.094 2(1). The ν 4 level, ν 0 = 337.604 14(5) cm −1, and its overtones nν 4, n = 2 and 3, are apparently unperturbed. Very good consistency was found with ab initio predicted molecular parameters, of which several were adopted in our fits when experimental data were not available.

Ground State Constants AK0, DK0, and HK0 of CD 3I

The ground state constants A K 0, D K 0, and H K 0 for the CD 3I molecule have been determined by combining the infrared data obtained from high-resolution spectra of the bands ν 6, ν 5 + ν 6 − ν 6, and ν 5 + ν 6. Using the lines from these bands, ground-state combination differences which differ in K by a value of 3 were calculated. From these different K values, ranging from 0 to 7, the following values have been obtained: A K 0 = 2.5962779(14) cm −1, D K 0 = 20.773(35) × 10 −6 cm −1, and H K 0 = 0.38(24) × 10 −9 cm −1.

Millimeter-Wave and High-Resolution Infrared Spectra of Monoisotopic SC80Se: Equilibrium, Ground State, and ν1, mν2, and nν3 Rovibrational Parameters

The Fourier transform infrared spectrum of monoisotopic SC80Se has been investigated in the ν2, ν3, 2ν2, 2ν3, and ν1 regions with a resolution between 3 and 4 × 10−3 cm−1. In addition, the millimeter-wave spectrum has been studied in the region 150 to 320 GHz, and ground and ν2 = 1 excited state transitions have been measured. Ground state constants, B0 = 2043.285 4(4) MHz and D0 = 146.53(5) Hz, have been determined from a merge of millimeter-wave data and ground state combination differences spanning J values up to 77 and 143, respectively. The band centers ν2 = 352.341 075(9) cm−1 and ν3 = 505.480 06(5)cm−1 have been determined. The rovibrational parameters of numerous overtone and combination levels (ν1νl22ν3) = 0200, 0220, 0310, 0330, 0400, 0420, 0002, and 0003 have been obtained from polynomial analyses whose standard deviations ranged from 0.7 to 3.5 × 10−4 cm−1. The 1000 level, νeff 1435.840 cm−1, is anharmonically perturbed by the 0400 level, with an avoided crossing at J = 55, and W12222 = 0.963 09(1) cm−1. Transitions to both the upper (E+) and lower (E−) sublevels of the dyad were observed for 1 ≤ J′ ≤ 117 and 4 ≤ J′ ≤ 171, respectively, and the deperturbed wavenumbers ν1 = 1435.542 76(2) and 4ν02 = 1432.725 00(3) cm−1 were derived. Furthermore, a local crossing of the E− and 0420 levels involving l-type resonance was observed at J = 91.