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Rotational assignment of the high-resolution fluorescence excitation spectrum of the 14NO3 radical in the B ∼ 2E′ ← X ∼ 2A2′ transition 0–0 band region located around 15,100 cm−1 was made with the help of the ground state combination differences and the observation of Zeeman effect. We successfully identified several rotational line series based on the newly obtained rotational assignments of 162 lines with |k″| ⩽ 15 and J′ ⩽ 18.5 quantum numbers, and we estimated the effective molecular constants of the excited vibronic states.

We have observed the infrared spectrum of (15)NO(3) by a high resolution Fourier transform infrared (FT-IR) spectrometer using the reaction of F atoms with H(15)NO(3). Five (2)E'-(2)A(2)' bands are identified in the 1850-3150 cm(-1) region. The rotational analyses indicate that these bands have the lower state in common, which coincides with the ground state of planar D(3h) symmetry. The upper (2)E' states more or less suffer from perturbations by close-lying dark states. Among them, those of the 2004, 2128, and 2492 cm(-1) bands are analyzed to determine molecular parameters in these states by fixing the ground-state constants to those derived by a combination difference method. The spin-orbit and Coriolis coupling constants in the (2)E' states are substantially different for different vibronic states. The vibrational assignments of NO(3) in the ground electronic state are discussed using experimental data heretofore available, supplemented by those obtained by the present study.

Two sets of vibrational satellites have been observed in the rotational spectrum of sodium tetrahydroborate NaBH4, and have been assigned to the non-degenerate, Na—BH4 stretching and the degenerate BH4 rocking (or internal rotation) states. The observation was extended from the J = 11 ← 10 up to J = 20 ← 19 transitions. The vibrational satellites showed anomalous K structure; higher-K lines of the non-degenerate state appeared at higher frequencies, in reverse to those of the ground state, whereas the spectra in the degenerate state exhibited a K pattern similar to but somewhat more widely spread than that of the ground state. These anomalies are ascribed to the Coriolis interaction between the two excited vibrational states. The spectra observed were analysed using a C3v symmetric-top rotational Hamiltonian, which took into account the Coriolis interaction explicitly. The A rotational constants, the energy difference δE between the two interacting vibrational states, and the first- and second-order Corio...

Rotationally resolved high-resolution fluorescence excitation spectra of (14)NO3 radical have been observed for the 662 nm band, which is assigned as the 0-0 band of the B̃(2)E' ←X̃(2)A2' transition, by crossing a single-mode laser beam perpendicularly to a collimated molecular beam. More than 3000 rotational lines were detected in 15,070-15,145 cm(-1) region, but it is difficult to find the rotational line series. Remarkable rotational line pairs, whose interval is about 0.0246 cm(-1), were found in the observed spectrum. This interval is the same amount with the spin-rotation splitting of the X̃(2)A2' (υ = 0, k = 0, N = 1) level. From this interval and the observed Zeeman splitting up to 360 G, seven line pairs were assigned as the transitions to the (2)E'(3/2) (J' = 1.5) levels and 15 line pairs were assigned as the transitions to the (2)E'(1/2) (J' = 0.5) levels. From the rotational analysis, we recognized that the (2)E' state splits into (2)E'(3/2) and (2)E'(1/2) by the spin-orbit interaction and the effective spin-orbit interaction constant was roughly estimated as -21 cm(-1). From the number of the rotational line pairs, we concluded that the complicated rotational structure of this 662 nm band of (14)NO3 mainly owes to the vibronic interaction between the B̃(2)E' state and the dark Ã(2)E″ state through the a2″ symmetry vibrational mode.

The microwave spectrum of CsO has been observed and analyzed, not only in the ground vibrational state, but also in the v=1–3 excited vibrational states. The CsO radical was generated by the reaction of N2O with Cs vapor, which was produced by the reaction of Li metal with CsCl at 500–530 °C. The observed spectra were found to conform to those expected for a 2Σ diatomic molecule, thereby establishing the ground electronic state of CsO to be of 2Σ. The observed rotational and centrifugal distortion constants yielded the equilibrium bond length and the harmonic vibrational frequency to be 2.300 745 (16) A and 356.78 (11) cm−1, respectively, based on the Born–Oppenheimer approximation. A careful examination of the observed spectral pattern definitely concluded that the spin-rotation interaction constant was positive, at variance with the expectation from a simple 2Σ/2Π two-states interaction. This observation was interpreted by assuming positive contributions from higher excited electronic states which super...

Microwave spectra of Ar– 28 SiH 4 , Ar– 29 SiH 4 , Ar– 30 SiH 4 , and Ar– 28 SiD 4 were recorded using a pulsed molecular beam Fourier transform microwave spectrometer. The K = 0 and K = 1 components of the J = 3 ← 2 through the J = 7 ← 6 transitions were measured and assigned in the 9–24 GHz region. For the primary 28 Si isotopic species, Ar– 28 SiH 4 and Ar– 28 SiD 4 , a K = 0, A symmetry, a K = 0, F symmetry, a doubly degenerate K = 1, E symmetry, and an l / K -doubled, K = 1, F symmetry rotational progression are observed at the ≈1 K rotational temperature of the supersonic expansion. The rotational constants for the K = 0, A state for Ar– 28 SiH 4 and Ar– 28 SiD 4 are B = 1700.40624(9) MHz and 1630.687073(22) MHz and the centrifugal distortion constants are D J = 29.089(3) and 20.0198(8) kHz and H J = −1.91(3) and −0.851(8) Hz, respectively, where type A expanded uncertainties with a coverage factor, k = 3, are given here and elsewhere. The values of the rotational constants for the K = 0, A , and F states and for the K = 1, E state are in good agreement with the infrared-determined values for Ar– 28 SiH 4 . The measured linear Stark effect of the E -state transitions was analyzed to give a dipole moment of 9.24(8) × 10 −32 C · m [0.0277(2) D].

The infrared spectrum of SiH2 was observed in the 5 μm region by using diode laser spectroscopy, and the three bands ν1, 2ν2, and ν3 were recorded and assigned. A separate analysis of the three bands yielded the band origins, 1995.9280, 1987.6938, and 1992.816 cm−1, respectively, thereby establishing that ν1 is higher than 2ν2, contrary to the result of a previous matrix study. The anharmonic resonances, both ν1/2ν2 Fermi and 2ν1/2ν3 Darling–Dennison, which were observed in the laser induced fluorescence spectra previously reported, were reanalyzed by removing the condition ν1

The rotational spectra of 85RbO in the ground- and the first excited vibrational states and of 87RbO in the ground vibrational state were observed in the millimeter- and submillimeter-wave region. The RbO radical was generated in a high-temperature absorption cell by the reaction of N2O with Rb vapor, which was produced in the cell by heating a mixture of RbCl and lithium metal to 500–550 °C. Analysis of the observed spectra yielded the rotational and centrifugal distortion constants, spin–rotation interaction constants, and hyperfine interaction constants. The bond length and the vibrational frequency were calculated from the rotational and centrifugal distortion constants to be 2.254 193 1 (15) A and 387.22 (20) cm−1, respectively, for 85RbO. The ground electronic state of RbO was confirmed to be 2Σ, and the low-lying 2Π state was estimated to be located at 650–700 cm−1 above the ground state by using a second-order perturbation expression with the vibrational energy in the denominator for the spin–rota...

Seven transient molecules, of which four are expected to play important roles primarily in deposition processes in plasma and three mainly in etching processes, were discussed on a basis of high-resolution vibration-rotation infrared spectra. A simple modification of infrared diode laser spectroscopy as referred to as kinetic spectroscopy allowed us to observe such spectra as functions of time. Applications of this spectroscopy to the diagnosis of three plasma processes were described to illustrate the potentiality as well as the versatility of the method: silane RF discharge plasma, methane RF and methanol ECR plasmas, and ECR etching plasma.

The rotational spectrum of the SiFCl molecule in the ground vibronic state was observed for the first time in the frequency region from 340 to 356 GHz. The analysis of the observed spectrum, which consisted of both a-type and b-type transitions, yielded rotational constants and centrifugal distortion constants of the 35Cl and 37Cl isotopic species in the ground state. The harmonic force field of SiFCl was derived from the centrifugal distortion constants and the inertial defects determined for both isotopic species and was used to calculate the vibrational frequencies of the molecule. The average structure in the ground vibrational state was determined to be r z ( SiF ) = 1.5960 A , r z ( SiCl ) = 2.0714 A , ϑz(FSiCl) = 100.85° and σr z ( SiCl )[ 35 Cl  37 Cl difference ] = 0.000065 A by using the observed rotational constants and the harmonic force field derived in the present study.

We have analyzed the near-infrared band of NO3 observed at 7602 cm−1 by using diode laser spectroscopy. Most of the spectral lines were recorded using source-frequency modulation. Zeeman modulation was found useful in selectively detecting some Q branch lines, which provided us with a clue to the assignment of the observed spectra. The band satisfied selection rules for a parallel band and was thus ascribed to a 2A1″–2A2′ vibronic component associated with the 2E′′–X 2A2′ electronic transition, namely, to a transition from the ground vibronic state to the A1″ vibronic state resulting from excitation of the degenerate in-plane bending mode in the 2E′′ electronically excited state manifold. The band was almost free of perturbations, except for some K=6 lines. The least-squares analysis of 581 assigned lines led to molecular parameters of the upper state, where ground-state parameters were fixed to those obtained from the infrared study previously reported [K. Kawaguchi, E. Hirota, T. Ishiwata, and I. Tanaka, J. Chem. Phys. 93, 951 (1990)]. The upper-state B rotational constant gave the effective N–O distance of 1.271 A, which is to be compared with 1.240 A in the ground vibronic state. The ebb spin–rotation interaction constant of the upper state was close in magnitude to that in the ground vibronic state, but of opposite sign. This observation indicates that the spin–rotation interaction is primarily caused by that between the 2E′′ excited and the ground electronic states.

The infrared spectrum of doubly deuterated methane CH2D2 has been recorded in the region from 1900 to 2400 cm-1 at almost Doppler-limited resolution by using two high-resolution Fourier transform spectrometers. The vibrational bands observed include 2nu4, nu4 + nu7, 2nu7, nu2, nu8, nu4 + nu9, and nu7 + nu9, which were analyzed by taking into account Coriolis and Fermi interactions among them and also those with nu4 + nu5, nu3 + nu7, and nu5 + nu7. Most of the centrifugal distortion constants were constrained to appropriate values, while the vibrational term value and three rotational constants in each of the seven excited states were adjusted along with Coriolis and Fermi interaction parameters by the least-squares analysis of the observed spectrum. The vibration-rotation interaction constants alphas thus determined for the nu2 and nu8 states were combined with those of other fundamental states already published to calculate the equilibrium C-H distance.

The lowest rotational transitions J = 1 ← 0 of NaBH 4 and KBH 4 were observed, using a Fourier transform microwave spectrometer combined with a laser ablation apparatus. Hyperfine structure has been observed at good resolution yielding precise values of the nuclear quadrupole coupling constants eQq for both the alkali metal and boron atoms. The eQq values of the alkali metals, −3.385(31) and −4.256(29) MHz for M = 23 Na and 39 K in M 11 BH 4 , respectively, are close to those in Na 35 Cl (−5.6698 MHz) and K 35 Cl (−5.656 MHz), indicating that NaBH 4 and KBH 4 are also ionic molecules. The boron eQq ’s are small, −0.670(53) and −0.722(59) MHz for Na 11 BH 4 and K 11 BH 4 , respectively, much smaller in magnitude than those reported for known boron-containing compounds, indicating that the BH 4 group retains a structure of approximate T d symmetry.

The gas-phase vibration-rotation spectrum of FDF− was observed in the 930 and 1460 cm−1 regions with a tunable diode laser spectrometer. The observed bands in the 930 cm−1 region were assigned to the v3 antisymmetric stretching and the v2 bending modes. The 1460 cm−1 region was assigned to the v1 + v3 combination band. The previous assignment of the 1397 cm−1 band was corrected to the 2v1 + v3 − v1 band. All observed transitions were analyzed simultaneously by including a Coriolis interaction between the v2 and v3 states to determine molecular constants in the ground as well as v2, v3, v1 + v3, 2v1 + v3, and v1 states. The fundamental frequencies were determined to be v2 = 928.7303(17) cm−1 and v3 = 934.1933(7) cm−1, with three standard deviations in parentheses. From the rotational constants obtained, the equilibrium F ··· F internuclear distance was calculated to be 2.277 52(10) A, which agreed with the value (2.277 71(9) A) of FHF− reported previously.

The rotational spectrum of the ClS2 free radical in the gaseous phase has been observed in the millimetre- and submillimetre-wave regions. The ClS2 radical was generated by a dc glow discharge in either S2Cl2 or SCl2. Both a- and b-type R-branch transitions, most of which were split into two fine structure components, were detected for both of the 35Cl and 37Cl isotopic species in the ground vibronic state. As expected from the small hyperfine interaction constants reported by an electron spin resonance (ESR) study, the hyperfine structure was resolved for none of the transitions observed in the present study. Analysis of the observed transition frequencies yielded rotational and centrifugal distortion constants and also spin–rotation interaction constants with their centrifugal corrections. The spin–rotation interaction constants obtained in the present study were consistent with g values of the ESR study. The rotational constants of the two isotopic species led to the structure parameters r(S—S) = 1.906 (7) Å, r(S—Cl) = 2.071 (5) Å, and θ(SSCl) = 110.3 (4)°. A harmonic force field was derived from the observed centrifugal distortion constants and inertial defects combined with the ν1 frequency reported in literature on electronic spectroscopy. This harmonic force field yielded the ν2 and ν3 frequencies (445 (21) and 213.0 (2) cm−1, respectively, for 35ClS2), which differed considerably from the values reported previously.

The microwave spectrum of dichlorosilylene in excited vibrational states has been measured in the millimetre- and submillimetre-wave regions. Rotational and centrifugal distortion constants were determined for the ν 1 , ν 2 , 2ν 2 and ν 3 excited states of the Si 35 Cl 2 isotopic species and for the ν 2 and 2ν 2 states of Si 35 Cl 37 Cl. Analysis of the Coriolis resonance between the ν 1 and ν 3 states of Si 35 Cl 2 yielded values of the D Coriolis interaction constant with F constrained, of two higher-order terms and also an accurate value [5.402338(95) cm −1 ] of the energy difference between the two excited vibrational states. The rotational constants of Si 35 Cl 2 in the first excited states of the three normal vibrations were combined with those of the ground vibrational state reported in a previous paper [M. T animoto et al., J. Chem. Phys . 91 , 2102 (1989)] to obtain the equilibrium structure, harmonic and cubic/third-order anharmonic potential constants.

The change in the centrifugal distortion constants of the allyl radical with the vibrational excitation to the ν 11 state was interpreted as being caused by the interaction of the ν 11 state with the overtone state of the ν 7 mode. This interpretation requires revision of the ν 7 frequency, in conformity with the recent results reported by Getty and co-workers (J. Am. Chem. Soc., 113 (1991) 801; Chem. Phys., 168 (1992) 357) using resonance Raman spectroscopy. The normal coordinate analysis was performed on the allyl radical based upon the vibrational assignment revised by Fjogstad and Ystenes (Spectrochim. Acta, Part A, 46 (1990) 47) and Getty and co-workers in order to calculate the inertial defect and centrifugal distortion constants for comparison with the observed values.

The fundamental vibrational band of the 7LiO radical in the ground electronic state X 2Πi was observed in a region from 720 to 850 cm−1 using a source frequency modulation infrared diode laser spectrometer. Radicals were generated in a high‐temperature cell by the reaction of lithium metal vapor with nitrous oxide. The observed spectrum was analyzed together with the radio‐frequency and microwave spectra already reported. It was found that the vibration‐rotation Hamiltonian employed in a previous paper was insufficient to fit all of the observed spectra simultaneously. The Hamiltonian was thus extended to include higher‐order corrections for the centrifugal distortion and Λ‐type doubling terms, and was used to derive molecular parameters.

Author Institution: Department of Chemical, Technolo gy, Kanagawa Institute of Technology; Department of Chemical, The Graduate University for Advanced Studies

Millimeter- and submillimeter-wave spectroscopy was applied to an alkali heterodimer molecule NaK. The NaK molecule was generated in a heated stainless steel pipe, which also served as an absorption cell. Rotational transitions of J = 14 to 69 were observed for the vibrational states of v = 0 to 6 in the ground electronic state. A set of Dunham coefficients which reproduced the observed transition frequencies within experimental errors were determined with much higher precision than in previous studies. The possibility of detecting NaK in the circumstellar atmosphere was briefly discussed.

The internal motion in MBH 4 , with M denoting an alkali atom, has been discussed theoretically by taking into account two internal degrees of freedom, the M-(BH 4 ) stretch and the BH 4 internal rotation, in addition to the overall rotation. The energy level expressions were derived to discuss characteristic features of the rotational spectra in the ground as well as in excited vibrational states. Particular attention was paid to splittings in the rotational spectra which are caused by the tunneling motion of the BH 4 group.

The 1492 cm−1 band of NO3 previously reported [J. Chem. Phys. 82, 2196 (1985); 93, 951 (1990)] exhibits some features in the upper state which are difficult to understand if the band is purely vibrational, i.e., the degenerate N–O stretching band in the ground electronic state. The two most conspicuous anomalies are a finite spin‐orbit coupling term which must be included in the Hamiltonian and a derived first‐order Coriolis coupling constant which is smaller than the calculated value. These anomalous features are explained by the vibronic interaction with excited 2E’ electronic states.

The infrared spectrum of NO 3 was observed in the 1300–2800 cm −1 region by a high-resolution FT-IR spectrometer using the reaction of F atoms with HNO 3 . Three 2 E′- 2 A′ 2 bands were newly observed in the 1927, 2024, and 2155 cm −1 region in addition to the 1492, 2518, and 2585 cm −1 bands observed previously by a diode-laser system. The 2024 and 2155 cm −1 bands were analyzed by using a D 3h Hamiltonian to derive molecular constants. It was found that the obtained spin—orbit and Coriolis coupling constants in the 2 E′ states are very different for different vibronic states. The vibronic assignments of these bands are discussed.

Ishiwata et al. [J. Chem. Phys. 82, 2196 (1985)] have recently observed an infrared diode laser spectrum of NO3 in the 1492 cm−1 region and have assigned it to the ν3 band in the X2A’2 state. However, some of the derived constants such as the Coriolis coupling and spin–rotation constants did not conform well with expected values. In the present study, the observation was extended so as to take combination differences, which led us to revise the previous assignment slightly and to remove all the anomalies in the lower (i.e., ground) state. A most important result of the present study is that a spin–orbit interaction constant aeff‖〈Lz〉‖ =0.17 cm−1 is indispensable to explain the spin splitting observed for the upper state. The first‐order Coriolis coupling constant of the upper state (ζ=0.19) remains essentially the same as in the previous study and differs considerably from the value calculated for the ν3 state (ζ=0.7). Possible explanations of these data are discussed in some detail to obtain more inform...

Determination des constantes moleculaires dans les etats vibrationnels fondamental et υ 3 =1

The nu1 and nu3 bands of D11BO and the nu1 band of D10BO were observed by using an infrared diode laser spectrometer. The DBO molecule was generated by an ac discharge in a mixture of BCl3, D2, O2, and He. As inferred previously, a strong Coriolis interaction was in fact found to take place between the nu1 and nu2 + nu3 states, and an analysis of the observed nu1 spectra, which explicitly took into account this Coriolis interaction, predicted the pure rotational transition frequencies of DBO in the nu1 state. Pure rotational lines were then detected by microwave spectroscopy, confirming the validity of the infrared assignment. In the microwave experiment DBO molecules were generated by a discharge in a mixture of B2D6 and O2. The three fundamental bands and a hot band of D11BO, as well as the nu1 and nu3 bands of D10BO, were subsequently recorded in emission with a Fourier transform infrared spectrometer. DBO molecules were generated by the reaction of D2 with HBO at temperatures above 800 degreesC in a ceramic tube furnace. All of the observed spectra were simultaneously subjected to a least-squares analysis to obtain molecular parameters in the ground, nu1, nu2, nu3, and nu2 + nu3 states. The results thus obtained improved the force field and molecular structure of the HBO/DBO molecules reported in a previous study (Y. Kawashima, Y. Endo, and E. Hirota, 1989, J. Mol. Spectrosc. 133, 116-127). Copyright 1998 Academic Press.

The pure rotational spectrum of CCl2 in the ground state was observed for the first time in the millimeter‐ and submillimeter‐wave region. The CCl2 molecule was generated directly in a free space cell by a dc glow discharge in CCl4 . Several transitions showed hyperfine splittings arising from the nuclear quadrupole coupling of two Cl atoms. Analysis of the observed spectrum yielded the rotational, centrifugal distortion, and nuclear quadrupole coupling constants of the C35 Cl2 species. The r0 structure was derived from the rotational constants to be r0 (C–Cl)=1.7157 A and θ0 (ClCCl)=109.2°. The ionic and π character of the C–Cl bond were estimated from the nuclear quadrupole coupling constants to be 0.26 and 0.32, respectively.

The dye laser excitation spectrum of the Swan band ( v ′ − v ″ = 1 − 0) has been observed with Doppler-limited resolution. The C 2 molecule was generated by the reaction of microwave discharge products of CF 4 with CH 4 . The high sensitivity of laser excitation spectroscopy has enabled us to observe not only ΔΩ = 0 transitions, but also ΔΩ = ± 1 transitions and to determine molecular constants including the spin-orbit coupling constant for both the d 3 Π g and a 3 Π u states. The parameters thus obtained for a 3 Π u were favorably compared with those previously obtained from the Ballik-Ramsay band. The present results on the d 3 Π g v = 1 state were combined with those of an earlier Fourier spectroscopic study on the Swan band ( v ′ − v ″ = 0 − 0) to derive equilibrium molecular constants for the d 3 Π g state. The contributions of the spin-rotation interaction and the centrifugal correction for the spin-orbit coupling to the energy levels in a 3 Π state have been discussed in detail.

The fine-structure spectra of 16O2 in the first excited vibrational state have been observed at room temperature with a double-modulation spectrometer. The spectra of an isotopic species 16O18O in the ground state are also observed in natural isotopic abundance. Revised energy formulas, which are derived as a slight extension of Tinkham and Strandberg's treatment, are used in the analyses, and much more accurate equilibrium molecular constants are determined; λ′e = 59 429.08 ± 0.11 MHz, μe = −252.265 ± 0.011 MHz, Be = 43 336.2 ± 1.5 MHz, and r e = 1.20748 ± 0.00005 A .

Optical–optical double resonance or stimulated emission pumping spectroscopy has been applied to the HCF molecule to obtain precise molecular constants in excited vibrational states associated with the ground electronic state. A cw dye laser excites HCF molecules to a single rotational level of the A1 A‘(000) state, and transitions induced by a second cw dye laser downward to rotational levels in excited vibrational states of the ground electronic state are observed as dips of the fluorescence from the A1 A‘(000) state. The signals are observed at sub‐Doppler resolution (about 0.002 cm−1 FWHM), but their wave numbers are determined only to the precision 0.003 cm−1 of the dye laser wave number measurement. Molecular constants in the (010) and (020) states are determined precisely by a conventional least‐squares analysis of the observed signals. The (100) state is found to interact with the (011) state through Coriolis coupling, and the spectral data obtained for the two states are analyzed simultaneously...

The ν3 fundamental band of CO2+ has been observed with infrared diode laser spectroscopy, while modulating a hollow cathode discharge in CO2 by a magnetic field. The band origin has been determined to be 1423.0821(8) cm−1. This anomalously low value has been explained in terms of a vibronic interaction between X 2Πg and A 2Πu through the ν3 vibration, as in the case of BO2.

“Forbidden” rotational transitions of NH 3 with the selection rules Δ J =0 and k =±1←∓2 were measured in the submillimeter-wave region. The C o rotational constant for the lower component of the inversion doublet in the ground vibrational state is obtained from the observed spectrum as 186 695.815±0.053 MHz. The observed line intensity agreed well with that calculated from the centrifugal-distortion-induced dipole moment.

The pure rotational spectrum of the isotopically substituted methoxy radical 13CH3O was observed in the millimeter‐ and submillimeter‐wave region. The 12CH3O radical was also studied in the same wavelength region and the molecular parameters of the previous work were reexamined. It was found necessary to add a few terms for the centrifugal distortion. The hyperfine coupling constants of the carbon nucleus were determined for the first time. With reference to the rotational constants of CD3O, the rs structure of the methoxy radical was determined.

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) A, 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.

The microwave spectrum of the fluoromethyl radical, CH2F, has been observed by using a source‐frequency modulation spectrometer with a 1 m long free space absorption cell. The CH2F radical was generated directly in the cell by the reaction of methyl fluoride with 2450 MHz discharge products of CF4. The a‐type R‐branch transitions, N=1 ← 0, 2 ← 1, and 3 ← 2 for the ground vibrational state and N=2 ← 1 and 3 ← 2 for the first excited state of the out‐of‐plane bending mode (ν4), have been observed; all of them were found to be split into fine and hyperfine components, and individual lines were measured precisely. The hyperfine structure observed for the ground state is consistent with electronic symmetry of B1 and with odd parity with respect to the reflection on the ‘‘molecular plane.’’ A relative intensity measurement shows that the v4=1 state of even parity is located 300 (30) cm−1 above the ground state. These observations suggest that the CH2F molecule is essentially planar, although the presence of a small hump at the planar configuration cannot be excluded.The microwave spectrum of the fluoromethyl radical, CH2F, has been observed by using a source‐frequency modulation spectrometer with a 1 m long free space absorption cell. The CH2F radical was generated directly in the cell by the reaction of methyl fluoride with 2450 MHz discharge products of CF4. The a‐type R‐branch transitions, N=1 ← 0, 2 ← 1, and 3 ← 2 for the ground vibrational state and N=2 ← 1 and 3 ← 2 for the first excited state of the out‐of‐plane bending mode (ν4), have been observed; all of them were found to be split into fine and hyperfine components, and individual lines were measured precisely. The hyperfine structure observed for the ground state is consistent with electronic symmetry of B1 and with odd parity with respect to the reflection on the ‘‘molecular plane.’’ A relative intensity measurement shows that the v4=1 state of even parity is located 300 (30) cm−1 above the ground state. These observations suggest that the CH2F molecule is essentially planar, although the presence of a s...

The pure rotational spectrum of the thiomethoxy radical CH3S was observed for the first time in the millimeter‐wave region. The radical was produced in a 0.5 m long free‐space cell by the reaction of CH3SH with 2450 MHz microwave discharge products of CF4. The rotational transitions were observed to be split into doublets by spin‐orbit interaction, and each component of the doublets further into K structures spread over several hundred MHz by vibronic Coriolis interaction and vibronic (2,2)‐ and (2,−1)‐type interactions which are characteristic of a symmetric‐top molecule in an orbitally degenerate 2E electronic state. The magnetic hyperfine structure due to the three protons was clearly resolved and was analyzed by taking into account the pseudodipolar interaction which had not been considered previously. Ground‐state molecular parameters were determined by least‐squares analyzing the observed spectrum, and the C–S bond length was estimated to be 1.791 A from the observed B rotational constant while assu...

The ν3 (CF stretching) band of the CH2F radical was observed with Doppler-limited resolution, by using infrared diode laser spectroscopy with Zeeman and discharge current modulation. The CH2F radical was generated directly in a multiple reflection absorption cell by the electrical discharge in CH2FCOOCH3. The observed spectrum was analyzed to yield the band origin of 1170.4165(6) cm−1 with one standard error in parentheses, in addition to the rotational constants, centrifugal distortion constants, and spin-rotation interaction constants in the v3 = 1 state.

Vibration-rotation transitions of the fundamental band have been observed for both C35Cl and C37Cl in the 2 Π 1 2 and 2 Π 3 2 states by using an infrared diode laser spectrometer with Zeeman modulation. A few lines of the “hot” band (v = 2 ← 1) have also been recorded for C35Cl. From an analysis of the observed spectra improved values were obtained for the vibrational harmonic frequency and anharmonicity constant, rotational constants, and Λ-doubling parameters. It was found necessary to take into account centrifugal distortion effects on the spin-orbit coupling constant A in the analysis, which gave ( dA dr ) e r e to be −176 ± 38 or −125 ± 38 cm−1, depending upon whether 2Σ− or 2Σ+ states contribute more to the Λ-type doubling. The equilibrium internuclear distance re was calculated from the derived rotational constants to be 1.64506 ± 0.00016 A.

The rotational spectrum of the SF radical in the 2 Π 1 2 state was observed by using a source-modulation microwave spectrometer with a 1-m-long discharge cell. The SF radical was generated directly in the cell by a dc discharge in an OCS CF 4 mixture. A previous measurement of the microwave spectrum in the 2 Π 3 2 state was also extended to higher-J transitions. The least-squares analysis of all the observed spectral lines gave the B0 rotational constant and the D0 centrifugal distortion constant to be 16 576.9140(46) and 0.02924(10) MHz, respectively, where the values in parentheses denote 2.5 times the standard deviations. The Λ-doubling constant pv was found to be extremely small, 3.409(44) MHz, and it was presumed that contributions of 2Σ+ and 2Σ− states to the Λ doubling cancel each other. All the four fluorine hyperfine coupling constants were also determined, from which the spin density on the F atom was calculated to be 0.13.

The pure rotational spectrum of the a 1 Δ SO radical in the vibrational states of ν up to 5 has been observed in the submillimeter-wave region of 300 to 400 GHz. The SO radical was produced by the excimer laser photolysis of Cl 2 SO at 193 nm, and its absorption signal was detected by a transient digitizer followed by a computer for signal processing. The present method is discussed as a means of studying short-lived molecules.

The time dependence of microwave absorption was measured for the J = 2-1 and J = 3-2 transitions of OCS under on- and off-resonant conditions utilizing Stark and source modulation, respectively. The two effective pressure parameters obtained under the two conditions, which correspond to (T 2 −1 + T 1 −1 ) 4πP and (2πT 2 P) −1 , respectively, according to the Bloch equation, are different beyond experimental error; the difference (T 2 −1 − T 1 −1 ) 2πP is 0.94 ± 0.38 (2.5σ) MHz/Torr for J = 2−1. This difference was also determined to be 1.19 ± 0.30 MHz/Torr from the dependence of the nutation frequency on the microwave power.

The (0, 1, 0)κ 2 Σ ← (0, 0, 0) 2 Π 3 2 vibration-rotation transition of BO 2 has been observed by infrared diode laser spectroscopy. The observed wavenumbers were combined with the spectral data on the (0, 1, 1) ← (0, 1, 0) band previously reported and were analyzed by the least-squares method to yield the ν 2 -band origin 633.8049(9) cm −1 and the spin uncoupling constants γ κ = 0.167 38(19) and 0.153 48(17) cm −1 , respectively, for the (0, 1, 1) κ 2 Σ and (0, 1, 0) κ 2 Σ states, with three standard deviations in parentheses. The effects of rovibronic interaction on the spin uncoupling constant and its centrifugal distortion correction term have been discussed in some detail. It has been found that the (0, 1, 1) κ 2 Σ state is perturbed by the (1, 2, 0)μ 2 Π 3 2 state through higher order rovibronic interaction.

The pure rotational spectrum of an unstable diatomic molecule, boron chloride (BCl), has been observed in the millimeter wave region. The BCl molecule was directly generated in a 3.7-m long free space absorp-tion cell by a d.c. glow discharge in BCl3. Rotational transitions of 11B35Cl and 11B37Cl in the ground vibrational state, which are split into a few components by the nuclear electric quadrupole interactions, have been observed and analyzed to yield molecular constants including the chlorine nuclear quadrupole coupling constant with high accuracy. The eQq constant thus determined is discussed along with those of other diatomic chlorides, to obtain information on the electronic structure of the molecules.

Using CO 2 and N 2 O lasers, we have measured and assigned nineteen ν 4 and nine ν 6 rotation-vibration resonances of the type Δ M = 0 and M = J . These transitions were combined with the zero-field pure rotational spectra in order to determine the two fundamental vibrational frequencies, the rotational constants of both excited states, the Coriolis coupling constant, and the dipole moments of each of the three states. The ground-state rotational constants and centrifugal distortion constants were taken from a microwave study and the centrifugal distortion constants of the excited states were assumed equal to those of the ground state. The following results were obtained (standard deviations in parentheses): ν 4 ν 6 ν 0 938.0345 (6) 989.2519 (18) (cm −1 ) A 139 579 (150) 143 323 (150) (MHz) B 31 873.6 (5) 32 379.5 (7) (MHz) C 26 242.9 (6) 25 994.4 (8) (MHz) ξ 64 (a) 136 178 (770) (MHz) μ 2.319 (10) 2.347 (4) (D) μ(ground state) 2.3464 (8) (D) The ν 0 and μ (ground-state) values agree with, but are more precise than other determinations, and the excited-state dipole moments are reported here for the first time. The values of some of the other parameters are consistent with those from a recent infrared spectrum.

A powerful method for detailed studies of the static and dynamic properties of molecules in highly excited vibrational states is presented. NH3 molecule is excited to the v=5 state in the N–H stretching mode by a pulsed dye laser and a subsequent transient change in the millimeter wave absorption due to the inversion transition in the excited state is observed before the distribution returns to thermal equilibrium. The determined inversion transition frequencies are more accurate by more than two digits than those reported in the previous work.

The CCl radical was generated by a dc glow discharge in CCl4, and rotational transitions of C35Cl in both 2 Π 1 2 and 2 Π 3 2 were observed in the mm-wave region by using a source modulation microwave spectrometer. From an analysis of the observed spectra the magnetic and electric quadrupole hyperfine coupling constants of the 35Cl nucleus were determined precisely. The Λ-doubling constant p0 was determined to be positive, indicating that unknown 2Σ− excited electronic states are making dominant contributions to the Λ doubling in the ground state. The previous diode-laser result [J. Mol. Spectrosc.85, 416–426 (1981)] was reanalyzed by using improved wavelength standards and by fixing the ground-state parameters to the present microwave values including the B0 rotational constant 20 797.1725(38) MHz. The vibration-rotation constant αB and the equilibrium bond length re were thus determined to be 0.006 768 2(48) cm−1 and 1.645 218(16) A, respectively, with 2.5 times standard deviations in parentheses. The spin density on the chlorine atom was estimated to be about 0.20 from the observed hyperfine coupling constants.