L-type Doubling Research Articles

Doppler-free ultraviolet excitation spectra of C ^1II_u–X^1Σ^ + _g in Na_2 by modulated population spectroscopy

The C1Πu state of Na2 has been studied in detail by cw UV Doppler-free excitation spectra from its ground state, simplified by modulated population spectroscopy. 270 levels of e parity and 180 levels of f parity with 11 ≤ υ ≤ 35 and 8 ≤ J ≤ 70 were measured with high resolution. The observations reveal that many of the e levels with 15 ≤ υ ≤ 24 are perturbed. A likely candidate for the perturbing state is the (3)Σ1u+ state. A set of Dunham coefficients was deduced to fit the spectroscopic data after deperturbation and used to construct the Rydberg–Klein–Rees potential for the C1Πu state. In addition, Λ-type doubling of the state was observed directly.

Λ-Doubling in the jet-cooled A-X emission spectrum of Cl2+

Several bands of the A-X emission spectrum of Cl2+ have been recorded at high resolution in a rotationally cold supersonic expansion of Cl2 and He excited with a corona discharge. Λ-type doubling has been observed for the first time in this system, confirming the identity of these bands as members of the Ω = 12 component of the electronic transition. Rotational constants have been obtained with higher precision than has previously been possible, allowing us to clarify some outstanding questions about the relative vibrational numbering of these bands.

Infrared diode laser spectroscopy of the SiF radical

The vibration-rotation spectrum of the SiF radical produced in a glow discharge of silicon tetrafluoride (SiF4) was observed using an infrared diode laser spectrometer. The SiF lines were discriminated from much stronger SiF2 lines by the discharge current modulation and Zeeman modulation techniques. Twelve and 15 lines belonging to the 2Π12 and 2Π32 spin states, respectively, were identified for the fundamental band in the ground electronic state. Most of the lines in the 2Π12 state were observed with splitting due to the Λ-type doubling. Precise molecular constants for the v = 1 state, including the rotational, centrifugal distortion, and spin-orbit coupling constants, were obtained from the least-squares analysis, in which the ground state constants were constrained as determined by microwave spectroscopy. The fundamental band origin thus obtained is 847.7205 ± 0.0005 cm−1, where the uncertainty corresponds to three standard deviations. The equilibrium bond length re is derived as 1.601018 ± 0.000003 A from the equilibrium rotational constant, Be = 0.581241 ± 0.000002 cm−1.

Diode laser spectroscopy of gas phase C5: The ν3 fundamental and associated hot bands

The spectrum of the linear carbon chain molecule C5 in the gas phase has been studied around 2170 cm−1, the region of the highest asymmetric stretching vibration ν3. The results were obtained using a tunable diode laser spectrometer and a cooled hollow cathode discharge in a flowing mixture of acetylene and helium. Four vibration–rotation bands were assigned and analyzed: the fundamental, a hot band arising from the v7=1, l=1 vibrational level, a second hot band arising from v7=2, l=0, and a third hot band tentatively ascribed to v5=1, l5=1. Small local perturbations were found to affect the upper vibrational states of two of the bands. Analysis of the data yielded accurate values for a number of molecular parameters for C5, e.g., the band origin ν3= 2169.4410(2) cm−1, the rotational constant, B0 =2557.63(9) MHz, and the l-type doubling parameters, q7=3.99(6) MHz, and q5=2.36(9) MHz. The value of q7 may be used to estimate a value of 118 cm−1 for the lowest bending frequency of the molecule. There is no evidence in C5 for quasilinear behavior such as that shown by C3 and C3O2.

The microwave spectrum of the LiO radical

The rotational spectra of the 7LiO radical in the v=0 and v=1 vibrational states were observed in the millimeter and submillimeter wave region. The LiO radical was generated by the reaction of lithium vapor with N2O directly in a high temperature absorption cell. The rotational and centrifugal distortion constants, Λ-type doubling constants, spin–orbit interaction constant, and hyperfine interaction constants were derived through analysis of the rotational spectra observed in the present study combined with the radio frequency spectra of Λ-type transitions reported by S. M. Freund et al. [J. Chem. Phys. 56, 1467 (1972)]. The LiO radical was confirmed to have a 2Πi ground electronic state with an exceptionally large Λ-type doubling constant, as in the case of NaO. A pure precession hypothesis applied to the observed p Λ-type doubling constant gives the Σ–Π energy difference to be 2565 cm−1.

The far-infrared laser magnetic resonance spectrum of the CD radical and determination of ground state parameters

The far-infrared laser magnetic resonance spectrum of the CD radical in the v = 0 level of the X 2Π state has been studied in detail. Twelve transitions which are accessible with currently available laser lines have been recorded. The measurements have been analyzed and subjected to a single least-squares fit using an effective Hamiltonian. The data provide primary information on the rotational and fine-structure intervals between the lowest rotational intervals. They also yield values for the Λ-type doubling and deuteron hyperfine splittings in the same levels. Combination of the measurements with the corresponding data for CH allows the two parameters, γ and A D, to be determined separately.

Stimulated emission pumping spectroscopy of jet-cooled C3

We report a dispersed fluorescence spectrum obtained for excitation of a ∑+u–∑+g vibronic band of C3 at 33 588 cm−1, part of a newly discovered electronic system. Rotationally resolved stimulated-emission-pumping spectra of jet-cooled C3 using this ∑+u intermediate state are presented for dumping to the 0v121 (1≤v2≤13) and 6v121 (1≤v2≤5) levels in the 1Σ+g ground state. Vibrational term energies, rotational constants, and l-type doubling parameters are determined for each level.

Detection of the NaO radical by microwave spectroscopy

The rotational spectrum of the NaO radical in the four lowest vibrational states was observed in the millimeter- and submillimeter-wave region. The NaO radical was generated by the reaction of the sodium vapor with N2O directly in a high-temperature absorption cell. Analysis of the observed spectra yielded the rotational and centrifugal distortion constants, Λ-type doubling constants, spin–orbit interaction constants, and hyperfine interaction constants in the four vibrational states. The NaO radical is clearly shown to have the 2Πi ground electronic state with an anomalously large Λ-type doubling constant and very small hyperfine interaction constants. The molecular constants derived are discussed in terms of the ionic character of the bond.

Microwave spectrum, molecular structure, and force field of HBO

The HBO molecule was generated as a transient intermediate in the reaction of diborane with oxygen induced by a dc discharge. The J = 3 ← 2 transition was observed for H10BO and was combined with the spectra already reported to derive the rotational, centrifugal distortion, and nuclear quadrupole coupling constants for this species. The rotational and centrifugal distortion constants were determined also for D11BO, D10BO, H11B18O, and H10B18O. The measurements were extended to rotational transitions of H11BO and H10BO in the ν1, ν2, 2ν2, and ν3 states and to those of D11BO and D10BO in the ν2, 2ν2, and ν3 states. The vibrational frequencies and the rotational, vibration-rotation, l-type doubling, and centrifugal distortion constants thus determined for the six isotopic species were simultaneously analyzed to derive the equilibrium molecular structure and the harmonic and third-order anharmonic potential constants of the HBO molecule. The equilibrium bond lengths thus obtained are re(HB) = 1.166 67(41) Å and re(BO) = 1.200 68(10) Å, and the substituted, average, and effective structures were also calculated for comparison.

Microwave spectroscopy of FCCCN in the ground and excited vibrational states

Microwave spectrum of fluorocyanoacetylene (FCCCN) produced by a glow discharge in pentafluorobenzonitrile (C 6F 5CN) was observed using a source-modulated spectrometer with a free-space absorption cell. Rotational transitions of FCCCN in the range of J = 9-8 to 20-19 were measured with an accuracy of 30 kHz for the ground state as well as for the vibrationally excited states, ν 5 (<CCN bend), ν 6 (<FCC bend), ν 7 (skeletal bend), 2 ν 6, ν 5 + ν 7, ν 6 + ν 7, 2 ν 7, 3 ν 7, and 4 ν 7. The rotational and centrifugal distortion constants obtained for the ground state are 2070.9571 ± 0.0006 MHz and 90.32 ± 0.95 Hz, respectively, where the uncertainties correspond to one standard deviation. The observed l-type doubling constants for the ν 5 (0.7718 ± 0.0002 MHz), ν 6 (0.9017 ± 0.0002 MHz), and ν 7 (2.0264 ± 0.0003 MHz) states agree with the values calculated from the harmonic force field. Anomalous behavior of the centrifugal distortion constants observed for some vibrational states was interpreted as due to the l-type resonance between sublevels with different l values. The unperturbed centrifugal distortion and l-type doubling constants and the intervals between sublevels were determined. Rotational transitions in the Σ + sublevel of the 2 ν 6 as well as the ν 5 + ν 7 state are perturbed by the Fermi resonance with the ν 4 (CC stretch) vibrational state.

Optogalvanic spectrum of CO. II. The rotational structure of the L 1Π state

The Q branch and P, R branches of the 4pπL 1Π–3sσB 1Σ+ transition of CO have been newly observed by high resolution and low resolution optogalvanic spectroscopy, respectively. The value of the Λ-type doubling constant in the L 1Π state has been determined as q=0.0213±0.0012 cm−1. An accidental perturbation was discovered in the Π− component of the L 1Π state. The Angstrom (0–3) and (0–4) bands were also observed.

The microwave spectra of CO in the electronically excited states (a 3Πr and a′ 3Σ+)

The rotational transitions of CO in the electronically excited states (a 3Πr and a′ 3Σ+) are observed in the millimeter and submillimeter wave regions. The vibrational satellites are detected up to v=6 for the a 3Πr state and up to v=2 for the a′ 3Σ+ state. The observed spectra are found to be perturbed by the interaction between the a 3Πr and a′ 3Σ+ states, and they are not fitted to conventional formulations for the 3Πr and 3Σ+ states within the experimental uncertainties. A simultaneous deperturbation analysis for the a 3Πr (v=0–7) states and the a′ 3Σ+(v=0–3) states is carried out by using the observed transition frequencies and the reported data of the Λ-type doubling rf transitions in the a 3Πr state. The detailed molecular constants are obtained for the a 3Πr and a′ 3Σ+ states. These constants show smooth change on the vibrational quantum number. This indicates that they are almost free from the interaction between the a 3Πr and a′ 3Σ+ states.

The ν3 band system of SCCCS: High-resolution Fourier transform and diode laser measurements

The high-resolution infrared spectrum of the ν 3 band system of carbon subsulfide, SCCCS, was measured around 2100 cm −1 using a Fourier transform interferometer and a tunable diode laser spectrometer. The linewidths (FWHH) in the Fourier transform spectrum were determined to be ca. 0.0060 cm −1 whereas the linewidths in the diode laser spectrum were 0.0036 cm −1. The rotational structure of the ν 3 fundamental and the first two hot bands associated with the low-lying CCC bending mode ν 7 were assigned. The adjusted effective constants for the l components of each band as well as constants taking the l-type doubling and resonance effects into account were determined. The band center of the ν 3 fundamental and the B 0 value were determined to be 2100.098908(58) and 0.03059602(31) cm −1, respectively. The analysis confirmed that SCCCS displays the dynamics of a linear molecule.

Rotational spectra of DCCCN in some excited vibrational states

We have observed and analyzed the millimeter-wave spectrum of deuterated cyanoacetylene (DCCCN) in 12 excited vibrational states. The Hamiltonian of K. M. T. Yamada, F. W. Birss, and M. R. Aliev ( J. Mol. Spectrosc. 112, 347–356 (1985)) has allowed the determination of accurate rotational and l-type doubling constants for the following isolated states: ( v 4, v 5, v 6, v 7) = (1001), (0001), (0002), (0003), (0010), (0100), (0101), (0011), and 0012). The anharmonic resonance between the (1000), (0020), and (0004) states has been observed and analyzed, yielding the unperturbed rotational constants and the Fermi interaction constant.

Velocity modulation infrared laser spectroscopy of negative ions: The (011)–(001) band of azide (N−3)

We have measured 43 transitions centered at 1972 cm−1 in the (011)–(001) bending hot band of the azide ion (N−3) using diode laser velocity modulation spectroscopy of an NH3/N2O discharge. The data, ranging from P(32) to R(40), were fit to a standard l-type doubling Hamiltonian through quartic terms. The l splittings in the spectrum were unusually large compared with similar molecules. Intensity measurements indicate that the vibrational and rotational degrees of freedom are equilibrated, unlike the case for isoelectronic NCO−. Additional lines of the ν3 fundamental have also been measured, which further refine the values of the ground state parameters.

Laser spectroscopic investigation of the van der Waals molecule NaKr84

The absorption spectrum of the van der Waals molecule NaKr due to the transition X 2Σ→A2Π has been observed with high resolution using a tunable single-mode cw dye laser and producing the molecules by means of supersonic expansion. About 600 lines due to the most abundant Kr-isotope Kr84 have been analyzed. The spectroscopic parameters of molecular rotation, of fine structure splitting and of λ-type doubling have been obtained for the vibrational levels v′=10⋅⋅⋅14 of the A 2Π state and for the level v″=0 of the X 2Σ state. The experimental positions of the band origins of the vibrational transitions are in satisfactory agreement with the results of model potential calculations. The equilibrium distances of the X 2Σ and of the A 2Π state of NaKr84 have been determined to be 4.919(7) and 3.02(9) Å, respectively. For the well depth we obtain values of (69±4), (790±60), and (750±60) cm−1 for X 2Σ, A 2Π1/2, and A 2Π3/2, respectively.

Infrared spectroscopy of NH+: An analysis of the perturbation between the X 2Π and a 4Σ− states

The v=1–0 vibration–rotation transitions in the X 2Π and a 4Σ− states as well as those between the two electronic states were observed with a difference frequency laser as a radiation source. The two electronic states (X 2Π and a 4Σ−) lie close together and interact each other strongly through the spin–orbit coupling. A merged least-squares fit was carried out with the present infrared transition wave numbers, some of the previous optical term values, and the recent far-infrared rotational transition frequencies to determine the spectroscopic parameters precisely. The equilibrium internuclear distance was obtained to be 1.0692±0.0002 and 1.0924±0.0001 Å for the X and a states, respectively. The Λ-type doubling transition frequencies were calculated for several of the lowest J states with the molecular constants obtained and the hyperfine coupling constants determined from the far-infrared transitions.

Microwave spectroscopy of HCO + and DCO + in excited vibrational states

The J = 3-2, 4-3, and 5-4 transitions of DCO + and the J = 3-2 and 4-3 transitions of HCO +, both in the ν 2, 2 ν 2, ν 1, and ν 3 states, were observed to derive the rotational, centrifugal distortion, and l-type doubling constants. The Fermi resonance between the ν 1 and 4 ν 2 0 states of DCO + was analyzed using the observed molecular constants of the ν 1, ν 2, and 2 ν 2 states. The effect of the discharge electric field was noticed on the ν 2 and 2 ν 2 spectra.

The vibrational assignment for the A 2Π–X 2Σ+ band system of the SiN radical: The 0–0 bands of 29SiN and 3SiN

The vibrational assignment for the A–X system of the SiN radical was reexamined by observing the spectra in the 5 μm region of 29SiN and 30SiN in natural abundance. The original assignment of Mulliken for the A state was found to be correct, rather than the one currently accepted, i.e., the 5 μm spectrum was assigned to the 0–0 band of the A–X system. The term value of the A state was thus modified to Te(A)=2032.4(1) cm−1 and the equilibrium internuclear distance in the A state was recalculated to be 1.641 879(20) Å, with the uncertainty in parentheses which was primarily due to that in Planck’s constant. The vibrational and isotopic variations observed for the Λ-type doubling and the spin–orbit interaction constants of the A state and for the spin–rotation interaction constants in the X state were explained by treating the electronic matrix elements of the spin–orbit interaction and of the orbital angular momentum between the A/X, B/A, and D/X states as parameters.

Infrared diode laser spectroscopic study of the active nitrogen. The electronic transition between the lowest singlet metastable states a 1Πg–a′ 1Σ−u, 0–0 band

The a 1Πg–a′ 1Σ−u, 0–0 band of the molecular nitrogen was observed in an electric discharge plasma of nitrogen using infrared diode laser spectroscopy at Doppler-limited resolution. Precise values were obtained for the rotational constants and the energy separation between the two electronic states. The effect of Λ-type doubling in the a 1Πg state was observed as small shifts of Q branch and P/R branch transitions to higher and lower frequencies, respectively, than those expected if Λ doubling were absent.