Contribution to the analysis of the predissociated rovibronic structure of the symmetric isotopomers 16O3 and 18O3 of ozone near 10,400 cm-1): [3A2(3(2)(0)) <-- X1A1(0(0)(0))] and 3B2 <-- X1A1

The absorption spectrum of ozone was recorded at low temperatures (down to -135 degrees C) by high resolution Fourier transform spectrometry and intra cavity laser absorption spectroscopy (ICLAS) near 10,400 cm-1. A preliminary analysis of the rotational structure of the absorption spectra of 16O3 and 18O3 shows that this spectral region corresponds to a superposition of two different electronic transitions, one with a very broad rotational structure, showing for the first time the asymmetric stretching frequency mode nu3 of the electronic state 3A2, the other formed by a completely diffuse band, probably the 2(1)(0) band of a new transition due to the triplet electronic state 3B2. Predissociation effects induce large broadening of the rotational lines for the transition centered at 10,473 cm-1 identified as the 3(2)(0) band of the 3A2 <-- X1A1 electronic transition. The rotational structure cannot be analyzed directly but instead the band contour method was used to confirm the symmetry of the transition and to estimate the spectroscopic constants for the 16O isotopomer. The origin of the band is at 10,473 +/- 3 cm-1 and the value of the 16O3(3A2) antisymmetric stretching frequency mode is equal to 460 +/- 2 cm-1. We believe that the diffuse band is due to the 3B2 state and is located at about 10,363 +/- 3 cm-1 for 16O3 and 10,354 +/- 3 cm-1 for 18O3. The isotopic rules confirm the different results obtained for 18O3 and 16O3.     

Jet cooled spectroscopy of H2DO+: Barrier heights and isotope-dependent tunneling dynamics from H3O+ to D3O+

The first high resolution spectroscopic data for jet cooled H2DO+ are reported, specifically via infrared laser direct absorption in the OH stretching region with a slit supersonic jet discharge source. Transitions sampling upper (0-) and lower (0+) tunneling states for both symmetric (nu1+ <-- 0+, nu1- <-- 0-, and nu1- <-- 0+) and antisymmetric (nu3+ <-- 0+ and nu3- <-- 0-) OH stretching bands are observed, where +/- refers to wave function reflection symmetry with respect to the planar umbrella mode transition state. The spectra can be well fitted to a Watson asymmetric top Hamiltonian, revealing band origins and rotational constants for benchmark comparison with high-level ab initio theory. Of particular importance are detection and assignment of the relatively weak band (nu1- <-- 0+) that crosses the inversion tunneling gap, which is optically forbidden in H3O+ or D3O+, but weakly allowed in H2DO+ by lowering of the tunneling transition state symmetry from D(3h) to C(2v). In conjunction with other H2DO+ bands, this permits determination of the tunneling splittings to within spectroscopic precision for each of the ground [40.518(10) cm(-1)], nu1 = 1 [32.666(6) cm(-1)], and nu3 = 1 [25.399(11) cm(-1)] states. A one-dimensional zero-point energy corrected potential along the tunneling coordinate is constructed from high-level ab initio CCSD(T) calculations (AVnZ, n = 3,4,5) and extrapolated to the complete basis set limit to extract tunneling splittings via a vibrationally adiabatic treatment. Perturbative scaling of the potential to match splittings for all four isotopomers permits an experimental estimate of DeltaV0 = 652.9(6) cm(-1) for the tunneling barrier, in good agreement with full six-dimensional ab initio results of Rajamaki, Miani, and Halonen (RMH) [J. Chem. Phys. 118, 10929 (2003)]. (DeltaV0 (RMH) = 650 cm(-1)). The 30%-50% decrease in tunneling splitting observed upon nu1 and nu3 vibrational excitations arises from an increase in OH stretch frequencies at the planar transition state, highlighting the transition between sp2 and sp3 hybridizations of the OHD bonds as a function of inversion bending angle.     

Photodissociation spectroscopy of stored CH+ and CD+ ions: analysis of the b 3Sigma(-)-a 3Pi system

We have measured the photodissociation spectrum of CH(+) and CD(+) molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b (3)Sigma(-)-a (3)Pi bands were observed as strong resonances because a large fraction of the ions in the metastable a (3)Pi(v=0) state were pumped to b (3)Sigma(-) levels and predissociated via the c (3)Sigma(+) state into C(+) and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH(+) and the 3-0 and 4-0 bands in CD(+), we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH(+). Combining all data delivers new, significantly adjusted equilibrium constants for the b (3)Sigma(-) and a (3)Pi electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b (3)Sigma(-) vibrational levels in CH(+) and compare them to a model. For the initial rovibrational distribution of the stored metastable CH(+) molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X (1)Sigma(+) ground state. New aspects of the spin-forbidden a (3)Pi-X (1)Sigma(+) radiative decay are discussed. Finally, we predict b (3)Sigma(-)-a (3)Pi absorption and a (3)Pi-X (1)Sigma(+) emission lines through which CH(+) in the metastable a (3)Pi(v=0) state might be detectable in astrophysical environments.     

Structure and dynamics of the electronically excited C 1 and D 0+ states of ArXe from high-resolution vacuum ultraviolet spectra

Vacuum ultraviolet spectra of the C 1 ← X 0(+) and D 0(+) ← X 0(+) band systems of ArXe have been recorded at high resolution. Analysis of the rotational structure of the spectra of several isotopomers, and in the case of Ar(129)Xe and Ar(131)Xe also of the hyperfine structure, has led to the derivation of a complete set of spectroscopic parameters for the C 1 and D 0(+) states. The rovibrational energy level structure of the C 1 state reveals strong homogeneous perturbations with neighboring Ω = 1 electronic states. The analysis of isotopic shifts led to a reassignment of the vibrational structure of the C 1 state. The observation of electronically excited Xe fragments following excitation to the C state rotational levels of f parity indicates that the C state is predissociated by the electronic state of 0(-) symmetry associated with the Ar((1)S(0)) + Xe(6s(')[1/2](0) (o)) dissociation limit. The observed predissociation dynamics differ both qualitatively and quantitatively from the behavior reported in previous investigations. An adiabatic two-state coupling model has been derived which accounts for the irregularities observed in the rovibronic and hyperfine level structure of the C 1 state. The model predicts the existence of a second state of Ω = 1 symmetry, supporting several tunneling/predissociation resonances located ~200 cm(-1) above the C 1 state.     

Fluorescence-dip infrared spectroscopy and predissociation dynamics of OH A 2Sigma+ (v = 4) radicals

Fluorescence-dip infrared spectroscopy, an UV-IR double-resonance technique, is employed to characterize the line positions, linewidths, and corresponding lifetimes of highly predissociative rovibrational levels of the excited A (2)Sigma(+) electronic state of the OH radical. Various lines of the 4 <--2 overtone transition in the excited A (2)Sigma(+) state are observed, from which the rotational, centrifugal distortion, and spin-rotation constants for the A (2)Sigma(+) (v = 4) state are determined, along with the vibrational frequency for the overtone transition. Homogeneous linewidths of 0.23-0.31 cm(-1) full width at half maximum are extracted from the line profiles, demonstrating that the N = 0 to 7 rotational levels of the OH A (2)Sigma(+) (v = 4) state undergo rapid predissociation with lifetimes of < or =23 ps. The experimental linewidths are in near quantitative agreement with first-principles theoretical predictions.     

Supersonically cooled hydronium ions in a slit-jet discharge: high-resolution infrared spectroscopy and tunneling dynamics of HD2O+

Jet-cooled high-resolution infrared spectra of partially deuterated hydronium ion (HD2O+) in the O-H stretch region (nu3 band) are obtained for the first time, exploiting the high ion densities, long absorption path lengths, and concentration modulation capabilities of the slit-jet discharge spectrometer. Least-squares analysis with a Watson asymmetric top Hamiltonian yields rovibrational constants and provides high level tests of ab initio molecular structure predictions. Transitions out of both the lower (nu3(+)<--0(+)) and the upper (nu3(-)<--0(-)) tunneling levels, as well as transitions across the tunneling gap (nu3(-)<--0(+)) are observed. The nu3(-)<--0(+) transitions in HD2O+ acquire oscillator strength by loss of D(3h) symmetry, and permit both ground-state-[27.0318(72) cm(-1)] and excited-state-[17.7612(54) cm(-1)]-tunneling splittings to be determined to spectroscopic precision from a single rovibrational band. The splittings and band origins calculated with recent high level ab initio six-dimensional potential surface predictions for H3O+ and isotopomers [X. C. Huang, S. Carter, and J. M. Bowman, J. Chem. Phys. 118, 5431 (2003); T. Rajamaki, A. Miani, and L. Halonen, J. Chem. Phys. 118, 10929 (2003)] are in very good agreement with the current experimental results.     

The (CH2)2O-H2O hydrogen bonded complex. Ab Initio calculations and Fourier transform infrared spectroscopy from neon matrix and a new supersonic jet experiment coupled to the infrared AILES beamline of synchrotron SOLEIL

A series of hydrogen bonded complexes involving oxirane and water molecules have been studied. In this paper we report on the vibrational study of the oxirane-water complex (CH(2))(2)O-H(2)O. Neon matrix experiments and ab initio anharmonic vibrational calculations have been performed, providing a consistent set of vibrational frequencies and anharmonic coupling constants. The implementation of a new large flow supersonic jet coupled to the Bruker IFS 125 HR spectrometer at the infrared AILES beamline of the French synchrotron SOLEIL (Jet-AILES) enabled us to record first jet-cooled Fourier transform infrared spectra of oxirane-water complexes at different resolutions down to 0.2 cm(-1). Rovibrational parameters and a lower bound of the predissociation lifetime of 25 ps for the v(OH)(b) = 1 state have been derived from the rovibrational analysis of the ν(OH)(b) band contour recorded at respective rotational temperatures of 12 K (Jet-AILES) and 35 K (LADIR jet).     

The visible absorption spectrum of OBrO, investigated by Fourier transform spectroscopy

By the utilization of a new laboratory method to synthesize OBrO employing an electric discharge, the visible absorption spectrum of gaseous OBrO has been investigated. Absorption spectra of OBrO have been recorded at 298 K, using a continuous-scan Fourier transform spectrometer at a spectral resolution of 0.8 cm(-1). A detailed vibrational and rotational analysis of the observed transitions has been carried out. The FTS measurements provide experimental evidence that the visible absorption spectrum of OBrO results from the electronic transition C(2A2)-X(2B1). Vibrational constants have been determined for the C(2A2) state (omega(1) = 648.3 +/- 1.9 cm(-1) and omega 2 = 212.8 +/- 1.2 cm(-1)) and for the X(2B1) state (omega 1 = 804.1 +/- 0.8 cm(-1) and omega 2 = 312.2 +/- 0.5 cm(-1)). The vibrational bands (1,0,0), (2,0,0), and (1,1,0) show rotational structure, whereas the other observed bands are unstructured because of strong predissociation. Rotational constants have been determined experimentally for the upper electronic state C(2A2). By modeling the band contours, predissociation lifetimes have been estimated. Further, an estimate for the absorption cross-section of OBrO has been made by assessing the bromine budget within the gas mixture, and atmospheric lifetimes of OBrO have been calculated using a photochemical model.     

Pressure broadening and fine-structure-dependent predissociation in oxygen B 3sigma(u)-, v = 0

Both laser-induced fluorescence and cavity ring-down spectral observations were made in the Schumann-Runge band system of oxygen, using a novel-type ultranarrow deep-UV pulsed laser source. From measurements on the very weak (0,0) band pressure broadening, pressure shift, and predissociation line-broadening parameters were determined for the B 3sigma(u)-, v = 0,F(i) fine-structure components for various rotational levels in O2. The information content from these studies was combined with that of entirely independent measurements probing the much stronger (0,10), (0,19), and (0,20) Schumann-Runge bands involving preparation of vibrationally excited O2 molecules via photolysis of ozone. The investigations result in a consistent set of predissociation widths for the B 3sigma(u)-, v = 0 state of oxygen.     

Prediction of the rovibrational emission spectroscopy of B2Σ(+)-X2Σ(+) system in 12C17O+

An analytical formula based on the Herzberg's conventional rovibrational energy levels for diatomic system is proposed by taking multiple differences of spectral lines to predict the R-branch high-lying rovibrational emission spectroscopy, where only 15 accurate known transition lines and rotational constants D(v'), D(v') are needed. Using the formula, the R(11ee) and R(22ff) branches of (0, 2) and (0, 3) transition bands in the B(2)Σ(+)-X(2)Σ(+) system of (12)C(17)O(+) are studied. The results show that not only the relatively lower order rovibrational transition lines given by experiments are reproduced but also the higher and the absent spectral lines are correctly predicted for each band.     

EPR and IR spectra of the FSO3 radical revisited: Strong vibronic interactions in the 2A2 electronic ground state

The previous controversy about the ground-state symmetry and contradictory vibrational analyses of FSO3 has been solved by a reinvestigation of its EPR and IR matrix spectra. The anisotropic EPR spectrum of FSO3 isolated in an argon matrix at 5 K is in agreement with an axial symmetry and an 2A2 electronic ground state. While the obtained hyperfine-coupling constants agree quite well to previous measurements in different environments, the g values may be affected by the large motion of the low-lying (162 cm(-1)) rocking mode of FSO3. For the first time measurements of the IR matrix spectra were extended to the far infrared region and to all 16/18 O isotopomers of FSO3. A new fundamental at 161.6 cm(-1) in Ar matrix and, for the nine strongest bands of FSO3, the isotopic 16/18 O pattern have been observed and analyzed. The four line pattern of the a1-type fundamental modes at 1052.7, 832.5, and 531.0 cm(-1) confirmed the C3v symmetry of FSO3 in the electronic ground state. The e-type fundamental modes at 931.6, 426.2, and 161.6 cm(-1) are unusually low in energy and in intensity due to vibronic interaction to the low-lying electronic excited 2E states. On the other hand, several combinations and overtones of e-type fundamentals are strongly enhanced due to vibronic interactions.     

High-resolution pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopic study of the two lowest electronic states of the ozone cation O3+

The pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of jet-cooled O3 has been recorded in the range 101,000-104,000 cm(-1). The origins of the X 1A1-->X+ 2A1 and X 1A1-->A+ 2B2 transitions could be determined from the rotational structure of the bands, the photoionization selection rules, the photoionization efficiency curve, and comparison with ab initio calculations. The first adiabatic ionization energy of O3 was measured to be 101,020.5(5) cm(-1) [12.524 95(6) eV] and the energy difference between the X+ 2A1 (0,0,0) and A+ 2B2 (0,0,0) states was determined to be DeltaT0=1089.7(4) cm(-1). Whereas the X-->X+ band consists of an intense and regular progression in the bending (nu2) mode observed up to v2+=4, only the origin of the X-->A+ band was observed. The analysis of the rotational structure in each band led to the derivation of the r0 structure of O3+ in the X+ [C2v,r0=1.25(2) A,alpha0=131.5(9) degrees ] and A+[C2v,r0=1.37(5) A,alpha0=111.3(38) degrees ] states. The appearance of the spectrum, which is regular up to 102,300 cm(-1), changes abruptly at approximately 102,500 cm(-1), a position above which the spectral density increases markedly and the rotational structure of the bands collapses. On the basis of ab initio calculations, this behavior is attributed to the onset of large-amplitude motions spreading through several local minima all the way to large internuclear distances. The ab initio calculations are consistent with earlier results in predicting a seam of conical intersections between the X+ and A+ states approximately 2600 cm(-1) above the cationic ground state and demonstrate the existence of potential minima at large internuclear distances that are connected to the main minima of the X+ and A+ states through low-lying barriers.     

Microwave-based structure and four-dimensional morphed intermolecular potential for HI-CO(2)

(Microwave spectra of the four isotopologue/isotopomers, HI-(12)C(16)O(2), HI-(12)C(18)O(2), HI-(12)C(18)O(16)O, and HI-(12)C(16)O(18)O, have been recorded using pulsed-nozzle Fourier transform microwave spectroscopy. In the last two isotopomers, the heavy oxygen atom tilted toward and away from the HI moiety, respectively. Only b-type Ka = 1 <-- 0 transitions were observed. Spectral analysis provided molecular parameters including rotational, centrifugal distortion, and quadrupole constants for each isotopomer. Then, a four-dimensional intermolecular energy surface of a HI-CO2 complex was generated, morphing the results of ab initio calculations to reproduce the experimental data. The morphed potential of HI-(12)C(16)O(2) had two equivalent global minima with a well depth of 457(14) cm(-1) characterized by a planar quasi-T-shaped structure with the hydrogen atom tilted toward the CO2 moiety, separated by a barrier of 181(17) cm(-1). Also, a secondary minimum is present with a well depth of 405(14) cm(-1) with a planar quasi-T-shaped structure with the hydrogen atom tilted away from the CO2 moiety. The ground state structure of HI-(12)C(16)O(2) was determined to have a planar quasi-T-shaped geometry with R = 3.7717(1) A, thetaOCI = 82.30(1) degrees , thetaCIH = 71.55(1) degrees . The morphed potential obtained is now available for future studies of the dynamics of photoinitiated reactions of this complex.     

Observation and rovibrational analysis of the intermolecular NH3 libration band nu9(1) of H3N-HCN

The high-resolution far-infrared absorption spectrum of the gaseous molecular complex H(3)N-HCN is recorded by means of static gas-phase Fourier transform far-infrared spectroscopy at 247 K, using a synchrotron radiation source. The spectrum contains distinct rotational structures which are assigned to the intermolecular NH(3) libration band nu9(1) (nu(B)) of the pyramidal H(3)N-HCN complex. A rovibrational analysis based on a standard semirigid symmetric top molecule model yields the band origin of 260.03(10) cm(-1), together with values for the upper state rotational constant B' and the upper state quartic centrifugal distortion constants D'(J) and D'(JK). The values for the upper state spectroscopic constants indicate that the hydrogen bond in the H(3)N-HCN complex is destabilized by 5% and elongates by 0.010 A upon excitation of a quantum of libration of the hydrogen bond acceptor molecule.     

The near infrared spectrum of ozone by CW-cavity ring down spectroscopy between 5850 and 7000 cm(-1): new observations and exhaustive review

Weak vibrational bands of (16)O(3) could be detected in the 5850-7030 cm(-1) spectral region by CW-cavity ring down spectroscopy using a set of fibered DFB diode lasers. As a result of the high sensitivity (noise equivalent absorption alpha(min) approximately 3 x 10(-10) cm(-1)), bands reaching a total of 16 upper vibrational states have been previously reported in selected spectral regions. In the present report, the analysis of the whole investigated region is completed by new recordings in three spectral regions which have allowed: (i) a refined analysis of the nu(1) + 3nu(2) + 3nu(3) band from new spectra in the 5850-5900 cm(-1) region; (ii) an important extension of the assignments of the 2nu(1)+5nu(3) and 4nu(1) + 2nu(2) + nu(3) bands in the 6500-6600 cm(-1) region, previously recorded by frequency modulation diode laser spectroscopy. The rovibrational assignments of the weak 4nu(1) + 2nu(2) + nu(3) band were fully confirmed by the new observation of the 4nu(1) + 2nu(2) + nu(3)- nu(2) hot band near 5866.9 cm(-1) reaching the same upper state; (iii) the observation and modelling of three A-type bands at 6895.51, 6981.87 and 6990.07 cm(-1) corresponding to the highest excited vibrational bands of ozone detected so far at high resolution. The upper vibrational states were assigned by comparison of their energy values with calculated values obtained from the ground state potential energy surface of (16)O(3). The vibrational mixing and consequently the ambiguities in the vibrational labelling are discussed. For each band or set of interacting bands, the spectroscopic parameters were determined from a fit of the corresponding line positions in the frame of the effective Hamiltonian (EH) model. A set of selected absolute line intensities was measured and used to derive the parameters of the effective transition moment operator. The exhaustive review of the previous observations gathered with the present results is presented and discussed. It leads to a total number of 3863 energy levels belonging to 21 vibrational states and corresponding to 7315 transitions. In the considered spectral region corresponding to up to 82% of the dissociation energy, the increasing importance of the "dark" states is illustrated by the occurrence of frequent rovibrational perturbations and the observation of many weak lines still unassigned.     

Improved determination of structural changes of 2-pyridone-(H2O)1 upon electronic excitation

The change of the 2-pyridone-water cluster (2PYH(2)O) structure upon electronic excitation is determined by a Franck-Condon analysis of the intensities in the fluorescence emission spectra obtained via excitation of three different vibronic bands as well as a structural fit based on the rotational constants of eight isotopomers that have been reported by Held and Pratt (J. Am. Chem. Soc., 1993, 115, 9708]. A total of 93 emission band intensities were fit, together with the changes of rotational constants of 8 isotopomers. The geometry change upon electronic excitation to the pipi* state can be described by a strong and unsymmetrical elongation of the hydrogen bonds, a contraction of the OH bond involved in the cyclic cluster arrangement, and an unsymmetrical ring deformation. The resulting geometry changes are interpreted on the basis of ab initio calculations.     

The absorption spectrum of H2: CRDS measurements of the (2-0) band, review of the literature data and accurate ab initio line list up to 35000 cm(-1)

Five very weak transitions-O(2), O(3), O(4), O(5) and Q(5)-of the first overtone band of H(2) are measured by very high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) between 6900 and 7920 cm(-1). The noise equivalent absorption of the recordings is on the order of α(min)≈ 5 × 10(-11) cm(-1) allowing for the detection of the O(5) transition with an intensity of 1.1 × 10(-30) cm per molecule, the smallest intensity value measured so far for an H(2) absorption line. A Galatry profile was used to reproduce the measured line shape and derive the line strengths. The pressure shift of the O(2) and O(3) lines was accurately determined from a series of recordings with pressure ranging between 10 and 700 Torr. From an exhaustive review of the literature data, the list of H(2) absorption lines detected so far has been constructed. It includes a total of 39 transitions ranging from the S(0) pure rotational line near 354 cm(-1) up to the S(1) transition of the (5-0) band near 18,908 cm(-1). These experimental values are compared to a highly accurate theoretical line list constructed for pure H(2) at 296 K (0-35,000 cm(-1), intensity cut off of 1 × 10(-34) cm per molecule). The energy levels and transition moments were computed from high level quantum mechanics calculations. The overall agreement between the theoretical and experimental values is found to be very good for the line positions. Some deviations for the intensities of the high overtone bands (V > 2) are discussed in relation with possible pressure effects affecting the retrieved intensity values. We conclude that the hydrogen molecule is probably a unique case in rovibrational spectroscopy for which first principles theory can provide accurate spectroscopic parameters at the level of the performances of the state of the art experimental techniques.     

Resonant two-photon ionization spectroscopy of jet-cooled OsC

The optical spectrum of diatomic OsC has been investigated for the first time, with transitions recorded in the range from 17 390 to 22 990 cm(-1). Six bands were rotationally resolved and analyzed to obtain ground and excited state rotational constants and bond lengths. Spectra for six OsC isotopomers, 192 Os 12C (40.3% natural abundance), 190 Os 12C(26.0%), 189 Os 12C(16.0%), 188 Os 12C(13.1%), 187 Os 12C(1.9%), and 186 Os 12C(1.6%), were recorded and rotationally analyzed. The ground state was found to be X 3 Delta 3, deriving from the 4 delta 3 16 sigma 1 electronic configuration. Four bands were found to originate from the X 3 Delta 3 ground state, giving B 0"=0.533 492(33) cm(-1) and r 0 "=1.672 67(5) A for the 192 Os 12C isotopomer (1 sigma error limits); two of these, the 0-0[19.1]2<--X 3 Delta 3 and 1-0[19.1]2<--X 3 Delta 3 bands, form a vibrational progression with Delta G' 1/2=953.019 cm(-1). The remaining two bands were identified as originating from an Omega"=0 level that remains populated in the supersonic expansion. This level is assigned as the low-lying A 3 Sigma 0+ (-) state, which derives from the 4 delta 2 16 sigma 2 electronic configuration. The OsC molecule differs from the isovalent RuC molecule in having an X 3 Delta 3 ground state, rather than the X 2 delta 4, 1 Sigma+ ground state found in RuC. This difference in electronic structure is due to the relativistic stabilization of the 6s orbital in Os, an effect which favors occupation of the 6s-like 16 sigma orbital. The relativistic stabilization of the 16 sigma orbital also lowers the energy of the 4 delta 2 16 sigma 2, 3 Sigma(-) term, allowing this term to remain populated in the supersonically cooled molecular beam.     

Infrared diode laser spectroscopy of jet-cooled NiCO, Ni(CO)3 (13CO), and Ni(CO3(C 18O)

Gas phase infrared spectroscopic investigations of the CO vibration of jet-cooled NiCO, Ni(CO)3(13CO), and Ni(CO)3(C18O) are reported. The spectra were obtained using a recently assembled pulsed-discharge slit-jet IR diode laser spectrometer. The rotationally resolved spectrum of NiCO was collected as it was formed in the discharge, while the spectra of Ni(CO)3(13CO) and Ni(CO)3(C18O) were recorded as they were destroyed. For NiCO, band origins of 2010.692 89(34) and 2010.645 28(23) cm(-1) were measured, along with values of B0=0.151 094(7) and 0.149 597(6) cm(-1) and B(1)=0.150 244(7) and 0.148 742(6) cm(-1) for 58NiCO and 60NiCO, respectively. The B0 values for these isotopologs were used to determine the two bond lengths in NiCO, giving r0 (Ni-C)=1.641(40) A and r0 (C-O)=1.193(53) A, in agreement with recent microwave measurements. The constants determined for Ni(CO)3(13CO) were upsilon0=2022.075 753(95) cm(-1), B"=0.034 736(2) cm(-1), and B'=0.034 688(2) cm(-1). For Ni(CO)3(C18O), upsilon0=2021.936 83(18) cm(-1), B"=0.033 764(4) cm(-1), and B'=0.033 710(4) cm(-1) were obtained. From these rotational constants, bond lengths of r0 (Ni-C)=1.839+/-0.007 A and r0 (C-O)=1.121+/-0.010 A were obtained. These values are discussed in relation to the bond lengths measured by electron and x-ray diffraction methods.     

Fourier transform infrared emission spectra of MgH and MgD

High resolution Fourier transform infrared emission spectra of MgH and MgD have been recorded. The molecules were generated in an emission source that combines an electrical discharge with a high temperature furnace. Several vibration-rotation bands were observed for all six isotopomers in the X (2)Sigma(+) ground electronic state: v=1-->0 to 4-->3 for (24)MgH, v=1-->0 to 3-->2 for (25)MgH and (26)MgH, v=1-->0 to 5-->4 for (24)MgD, v=1-->0 to 4-->3 for (25)MgD and (26)MgD. The new data were combined with the previous ground state data, obtained from diode laser vibration-rotation measurements and pure rotation spectra, and spectroscopic constants were determined for the v=0 to 4 levels of (24)MgH and the v=0 to 5 levels of (24)MgD. In addition, Dunham constants and Born-Oppenheimer breakdown correction parameters were obtained in a combined fit of the six isotopomers. The equilibrium vibrational constants (omega(e)) for (24)MgH and (24)MgD were found to be 1492.776(7) cm(-1) and 1077.298(5) cm(-1), respectively, while the equilibrium rotational constants (B(e)) are 5.825 523(8) cm(-1) and 3.034 344(4) cm(-1). The associated equilibrium bond distances (r(e)) were determined to be 1.729 721(1) A for (24)MgH and 1.729 157(1) A for (24)MgD.