High resolution spectroscopy of sulfur trioxide and carbon suboxide

High resolution spectroscopy was used to study the properties of two simple polyatomic molecules, sulfur trioxide, SO₃, and carbon suboxide, C₃O₂. The fundamental modes and several hot bands of the ¹⁸O isotopic fonns of SO₃ (³²S¹⁸O₃ and ³⁴S¹⁸O₃) have been investigated using both infrared spectroscopy and coherent anti-Stokes Raman scattering spectroscopy (CARS). The Ramanactive symmetric stretching mode, vt, shows complex Q-branch patterns due to indirect Coriolis couplings, l-resonances, and Fermi resonances with infrared inaccessible v₂, v₄ combination/overtone levels. ¹⁸O isotopic substitution changes the character of these interactions in such a way that their effect on the v1 CARS spectrum is unique among the different isotopomers studied. Accurate rovibrational constants are determined for all of the mixed states for the first time, leading to deperturbed values for the vt band origin of 1004.661(24) and 1004.693(23) for ³⁴S¹⁸O3 and ³²S¹⁸O₃ respectively. The strong Coriolis coupling is very noticeable in these species due to the close proximity of the v₂ and v₄ fundamental vibrations. The effect that this and other interaction terms have on the vt CARS spectrum of ³⁴S¹⁸O₃ is examined by selectively turning off the coupling between the hot bands. A global force field analysis was performed with the fundamental frequency values of all of the isotopomers studied that revealed a counterintuitive trend in the bond lengths between sulfur oxide species. In addition, band center frequencies for all the mixed ¹⁶O-¹⁸O isotopic species are computed. High-resolution CARS Spectroscopy was also used to study the v₁ symmetric CO stretching mode of the quasi-linear molecule carbon suboxide, C₃O₂. Q-branches are seen that originate from the ground state and from thermally populated levels of the unusually low frequency v₇ bending mode. The intensity variation of these on cooling to about 110 K in a jet expansion requires reversal of the order of assignment given in a previous Raman study at low resolution. The identification of the v₁ Σg⁺ ← Σg⁺ transition from the ground state is confirmed by the absence of Jodd Q-branch lines in the resolved CARS spectrum. Analysis of this band leads to vibration-rotation parameters (in cm⁻¹) of v₁ = 2199.9721(6), (B'-B") = 2.029(6) x10⁻⁴. Other transitions originating from higher v₇ levels occur at only slightly lower wavenumber values, indicating that the ground state barrier to linearity (22 cm⁻¹) increases only 1 to 2 cm⁻¹ when the CO symmetric stretch is excited

High-resolution infrared studies of the ν10, ν11, ν14, and ν18 levels of [1.1.1]propellane

This paper is a continuation of earlier work in which the high resolution infrared spectrum of [1.1.1]propellane was measured and its k and l structure resolved for the first time. Here we present results from an analysis of more than 16,000 transitions involving three fundamental bands v₁₀ (E' - A'₁), v₁₁ (E' - A'₁), v₁₄ (A"₂ - A'₁) and two difference bands (v₁₀–v₁₈) (E' - E") and (v₁₁ - v₁₈) (E' - E"). Additional information about v₁₈ was also obtained from the difference band (v₁₅ + v₁₈) - v₁₈ (E' - E") and the binary combination band (v₁₅ + v₁₈) (E' - A'₁). Through the use of the ground state constants reported in an earlier paper [1], rovibrational constants have been determined for all the vibrational states involved in these bands. The rovibrational parameters for the v₁₈ (E") state were obtained from combination–differences and showed no need to include interactions with other states. The v₁₀ (E') state analysis was also straight-forward, with only a weak Coriolis interaction with the levels of the v₁₄ (A"₂) state. The latter levels are much more affected by a strong Coriolis interaction with the levels of the nearby v₁₁ (E') state and also by a small but significant interaction with another state, presumably the v₁₆ (E") state, that is not directly observed. Gaussian calculations (B3LYP/cc-pVTZ) computed at the anharmonic level aided the analyses by providing initial values for many of the parameters. These theoretical results generally compare favorably with the final parameter values deduced from the spectral analyses. Finally, evidence was obtained for several level crossings between the rotational levels of the v₁₁ and v₁₄ states and, using a weak coupling term corresponding to a Δk = ±5, Δl = ∓1 matrix element, it was possible to find transitions from the ground state that, combined with transitions to the same upper state, give a value of C₀ = 0.1936515(4) cm⁻¹. This result, combined with the value of B₀ = 0.28755833(14) cm⁻¹ reported earlier [1], yields a value of 1.586277(3) Å for the length of the novel axial CC bond in propellane

THE HIGH-RESOLUTION INFRARED ANALYSIS OF BROMOMETHANE BELOW 1800 cm−1

High Resolution infrared spectra of six isotopomers of bromomethane (CH$_{3}$Br, CD$_{3}$Br, $^{13}$CH$_{3}$Br – with the $^{79}$Br and $^{81}$Br isotopes for each isotopomer) have been recorded at the Pacific Northwest National Laboratory. Here, we will present an analysis of fundamental, overtone and combination vibrational states for CH$_{3}$Br below 1811 \wn. Previous high-resolution work in this region for bromomethane focused mainly on obtaining frequency positions and line strengths for atmospheric sensing purposes. However, our work on this molecule focuses on obtaining precise rovibrational parameters that will serve as a foundation for the analysis of higher energy combination and overtone bands involving these states. These precise measurements facilitate the identification of subtle rotational and vibrational interactions that have been theoretically predicted, but have never before been characterized. Specifically, the Fermi resonance between \nub{5} (E) and \nub{3}+\nub{6} (E) is identified as well as a weak Coriolis interaction between \nub{2} (A$_{1}$) and \nub{3}+\nub{6} (E). The 3\nub{3} vibrational state has been analyzed for the first time, and hyperfine splittings similar to those found in CH$_{3}$I for low \textit{K, J} levels have also been observed

HIGH RESOLUTION SPECTRAL MEASUREMENTS ON ENRICHED 10BF3^{10}BF_{3} FROM 400 TO 4000cm−14000 cm^{-1}

Author Institution: Pacific Northwest National LaboratoryWe have been engaged in the measurement and analysis of high-resolution infrared spectra of enriched samples of $^{10}BF_{3}$ and $^{11}BF_{3}$. The Fourier transform spectrometer at the Pacific Northwest National Laboratory (PNNL) facilities has been used to obtain measurements that range in resolution from 0.0015 to $0.0035 cm^{-1}$ with pathlengths of up to 32 m. Depending on the symmetry of the vibrational state, where allowed, the $A_{1}-A_{2}$ rotational splittings of the lowest K levels were observed and measured. At this time, 21 combination/overtone states have been measured so that almost all of the quadratic anharmonic vibrational constants have been determined. Our spectra also make it possible to directly characterize the $\nu_{1}$ state for the first time by means of the transitions $(110^{0}0^{0})-(000^{0}0^{0}) A^{\prime\prime}_{2}-A^{\prime}_{1}$ and $(110^{0}0^{0})-(100^{0}0^{0}) A^{\prime\prime}_{2}-A^{\prime}_{1}$. A number of weak interactions were observed that help to locate levels that could not be observed directly as transitions from the ground state. For example, the $(001^{1}1^{1})^{2} E^{\prime}$ level is perturbed through l-type resonance coupling with the $(001^{\pm 1}1^{\mp 1})^{0} A^{\prime}_{1}$ and $A^{\prime}_{2}$ vibrational levels. In this case the $A^{\prime}_{1}$ vibrational level is nearly $16 cm^{-1}$ above the $A^{\prime}_{2}$ vibrational level. Rovibrational constants are deduced for the combination/overtone states, and eventually, we expect to be able to give an improved set of ground state rotational constants. Without counting the transitions in the fundamental bands, there are over 18,000 transitions included in the least-squares fits made at this time

ANALYSIS OF ROTATIONAL STRUCTURE IN THE HIGH-RESOLUTION INFRARED SPECTRUM OF {\em cis}-1,3,5-HEXATRIENE

Author Institution: Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074; Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352The high-resolution infrared spectrum has been recorded for two C-type bands of {\em cis}-1,3,5-hexatriene. The resolution (0.0013 cm$^{-1}$) and the Doppler width (0.0012 cm$^{-1}$ at 900 cm$^{-1}$) are barely adequate for observing detailed rotational structure of this heavy molecule in a spectrum recorded at room temperature. An additional complication is the extensive hot band structure arising from excited states of the low frequency C-C torsional modes. A preliminary analysis of rotational structure yielded $^{R}$$R$$_{K}$ and $^{P}$$P$$_{K}$ series in each of the two bands, centered at 908 cm$^{-1}$ and 586 cm$^{-1}$. However, ground state combination differences (GSCDs) failed to fit a rotational Hamiltonian. Subsequent microwave spectroscopic measurements gave ground state rotational constants. Reliable GSCDs computed from the ground state rotational constants led to revisions in assignments of some of the sub-band series in the infrared spectrum and to a convincing assignment

ANALYSIS OF HIGH-RESOLUTION INFRARED SPECTRA OF 11^{11}BF3_3 FOR VIBRATIONAL STATES BETWEEN 1600 AND 4300 cm−1^{-1}

Author Institution: 15012 24th Ave. S.E., Mill Creek WA, 98012; Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-88, Richland, WA 99352 (PNNL is operated for the US; Department of Energy by the Battelle Memorial Institute under contract DE-AC05-76RL0 1830)Last year at this Symposium (RX02) we presented spectroscopic measurements and ro-vibrational analysis for vibrational states of $^{11}$BF$_3$ below 1600 cm$^{-1}$. This year we present measurements and analysis for vibrational states of $^{11}$BF$_3$ up to 4300 cm$^{-1}$. Measurements were made of an isotopically enriched sample using a Bruker IFS 120HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory. Spectra were recorded with resolutions ranging from 0.0015 to 0.0035 cm$^{-1}$ and pathlengths up to 32 m. The combination states in the following sets of interacting states have been either observed directly from a transition or determined indirectly by its perturbative affects on observed states: 102$^{2}$0$^{0}$ (3783.85162(8) cm$^{-1}$), 102$^{0}$0$^{0}$ (3756.085 cm$^{-1}$), 101$^{-1}$3$^{3}$ (3763.14(16) cm$^{-1}$), 002$^{0}$2$^{2}$ (3830.233(50) cm$^{-1}$); 200$^{0}$1$^{1}$ (2240.94976(3) cm$^{-1}$), 120$^{0}$0$^{0}$ (2264.327(10) cm$^{-1}$); 300$^{0}$1$^{1}$ (3118.20602(6) cm$^{-1}$), 220$^{0}$0$^{0}$ (3141.688(13) cm$^{-1}$); 110$^{0}$1$^{1}$ (2050.11053(7) cm$^{-1}$), 030$^{0}$0$^{0}$ (2081.12683(6) cm$^{-1}$); 010$^{0}$2$^{0}$ (1652.35840(7) cm$^{-1}$), 010$^{0}$1$^{2}$ (1652.73764(5) cm$^{-1}$); 101$^{1}$0$^{0}$ (2336.2009(29) cm$^{-1}$), 100$^{0}$3$^{1,3}$ (2311.519(15) cm$^{-1}$); 201$^{1}$0$^{0}$ (3216.2986(13) cm$^{-1}$), 200$^{0}$3$^{1,3}$ (3188.650(76) cm$^{-1}$); (001$^{1}$1$^{1}$)$^{0,2}$ (1931.87377(14) cm$^{-1}$), (000$^{0}$4$^{0,2,4}$) (1921.996(11) cm$^{-1}$); (101$^{1}$1$^{1}$)$^{0,2}$ (2810.69018(8) cm$^{-1}$), (100$^{0}$4$^{0,2,4}$) (2787.31 cm$^{-1}$); (201$^{1}$1$^{1}$)$^{0,2}$ (3687.1503(10) cm$^{-1}$). The 003$^{1}$0$^{0}$ $-$ 000$^{0}$0$^{0}$ transition was observed near 4310 cm$^{-1}$ and was treated as an unperturbed perpendicular band except for the {\em l}-type resonance between the {\em k} $=1$, {\em l} $=1$ and {\em k} $=-1$, {\em l} $=-1$ levels. Effects from other perturbations are thought to be too small to be observed. An infrared forbidden transition 011$^{1}$0$^{0}$ $-$ 000$^{0}$0$^{0}$, E$^{\prime\prime }$ $-$ A$_1^{\prime }$, was also observed near 2140 cm$^{-1}$. The transitions obey electric dipole allowed selection rules $\Delta${\em k} $=\pm2$, $\Delta${\em l} $=\mp1$. Intensity comes from a term in the dipole moment operator that governs the intensity of the 002$^{2}$0$^{0}$ $-$ 000$^{0}$0$^{0}$ transition and to a lesser extent from terms that govern the intensity of the 001$^{1}$1$^{1}$ $-$ 000$^{0}$0$^{0}$ transition and the fundamentals. A detailed discussion of the interactions and the fit spectroscopic constants will be presented for the vibrational states as well as the Hamiltonian used to derive them

QUANTITATIVE IR SPECTRA AND VIBRATIONAL ASSIGNMENTS OF CH2_2I2_2, AN ATMOSPHERIC AEROSOL PRECURSOR

Author Institution: Pacific Northwest National Laboratory, P.O. Box 999, MSIN K8-88, Richland, WA 99354\maketitle As part of the Northwest Infrared (NWIR) database of quantitative infrared spectra, we have recently completed quantitative spectra of diiodomethane, CH$_2$I$_2$. Photolysis of this molecule in the presence of ozone, O$_3$, has been suggested as an immediate precursor to new particle formation over the oceans, particularly in coastal areas. Combined with the quantitative medium (0.1 cm$^{-1}$) resolution vapor-phase IR spectra, liquid-phase IR and FT-Raman spectra, as well as \it{ab initio} \rm calculations have been used to update and extend the vibrational assignments of earlier workers. Two strong b$_2$ symmetry A-type bands at 584 and 1114 cm$^{-1}$ are observed, but are not resolved at 760 Torr and appear as B-type. In contrast, the b$_1$ symmetry C-type bands near 5953, 4426 and 3073 cm$^{-1}$ are resolved with rotational structure, including Q-branches with widths $<$ 1 cm$^{-1}$. Potential use of these bands for atmospheric monitoring will be discussed

ANALYSIS OF ROTATIONAL STRUCTURE IN THE HIGH-RESOLUTION INFRARED SPECTRUM OF CIS,CIS-1,4-DIFLUOROBUTADIENE

Author Institution: Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074; Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-88, Richland, WA 99352We seek an equilibrium structure {\it cis,cis}-1,4-difluorobutadiene. Rotational structure of a C-type band centered at 762.8 cm$^{-1}$ in the high-resolution infrared spectrum (0.0015 cm$^{-1}$) has been analyzed as a first step. A sequence of strong hot bands of the torsional mode (78 cm$^{-1}$) complicate the analysis of this band. Provisional ground state rotational constants are reported. The spectrum of a second C-type band at 328 cm$^{-1}$ may also be analyzable. Ground state rotational constants for a full set of isotopomers are needed. A procedure for synthesizing these species is being explored