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The carbon chain ions HC 3 O + and HC 3 S + – longer variants of the famous 'X-ogen' line carrier HCO + – have been observed for the first time using two cryogenic 22-pole ion trap apparatus (FELion, Coltrap) and two different light sources: the Free Electron Laser for Infrared eXperiments (FELIX), which was operated between 460 and 2500 cm − 1 , and an optical parametric oscillator operating near 3200 cm − 1 ; signals from both experiments were detected by infrared predissociation action spectroscopy. The majority of vibrational fundamentals were observed for both ions and their wavenumbers compare very favourably with results from high-level anharmonic force field calculations performed here at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations, CCSD(T). As the action scheme employed here probes the Ne-tagged weakly bound variants, Ne–HC 3 O + and Ne–HC 3 S + , corresponding calculations of these systems were also performed. Differences in the structures and molecular force fields between the bare ions and their Ne-tagged complexes are found to be very small. [ABSTRACT FROM AUTHOR]

The molecular structure of trans, planar hydridotrioxygen (HOOO) has been examined by means of isotopic spectroscopy using Fourier transform microwave as well as microwave-millimeter-wave double resonance techniques, and high-level coupled cluster quantum-chemical calculations. Although this weakly bound molecule is readily observed in an electrical discharge of H2O and O2 heavily diluted in an inert buffer gas, we find that HOOO can be produced with somewhat higher abundance using H2 and O2 as precursor gases. Using equal mixtures of normal and 18O2, it has been possible to detect three new isotopic species, H18OOO, HO18O18O, and H18O18O18O. Detection of these species and not others provides compelling evidence that the dominant route to HOOO formation in our discharge is via the reaction OH + O2 → HOOO. By combining derived rotational constants with those for normal HOOO and DOOO, it has been possible to determine a fully experimental (r0) structure for this radical, in which all of the structural parameters (the three bond lengths and two angles) have been varied. This best-fit structure possesses a longer central O-O bond (1.684 Å), in agreement with earlier work, a markedly shorter O-H bond distance (0.913 Å), and a more acute ∠HOO angle (92.4°) when compared to equilibrium (re) structures obtained from quantum-chemical calculations. To better understand the origin of these discrepancies, vibrational corrections have been obtained from coupled-cluster calculations. An empirical equilibrium (reemp) structure, derived from the experimental rotational constants and theoretical vibrational corrections, gives only somewhat better agreement with the calculated equilibrium structure and large residual inertial defects, suggesting that still higher order vibrational corrections (i.e., γ terms) are needed to properly describe large-amplitude motion in HOOO. Owing to the high abundance of this oxygen-chain radical in our discharge expansion, a very wide spectral survey for other oxygen-bearing species has been undertaken between 6 and 25 GHz. Only about 50% of the observed lines have been assigned to known hydrogen-oxygen molecules or complexes, suggesting that a rich, unexplored oxygen chemistry awaits detection and characterization. Somewhat surprisingly, we find no evidence in our expansion for rotational transitions of cis HOOO or from low-lying vibrationally excited states of trans HOOO under conditions which optimize its ground state lines. [ABSTRACT FROM AUTHOR]

The rotational spectra of two small silicon sulfides, silanethione H2SiS and the disilicon sulfide ring Si2S, have been detected in the centimeter band by Fourier transform microwave spectroscopy of a molecular beam; lines of H2SiS were also observed in the millimeter band up to 377 GHz in a glow discharge. Precise rotational and centrifugal distortionconstants have been determined for the normal and a number of the more abundant rare isotopic species of both closed-shell molecules. Theoretical equilibrium (re) structures of H2SiS and Si2S were derived from coupled-cluster calculations that included triple and quadruple excitations, core correlation, and extrapolation to the basis-set limit. The re structures agree to within 5×10-4 Å and 0.1°with empirical equilibrium (reemp) structures derived from the experimental rotational constants, combined with theoretical vibrational and electronic corrections. Both H2SiS and Si2S are good candidates for radioastronomical detection in the circumstellar shells of evolved carbon-rich stars such as IRC+10216, because they are fairly polar and are similar in composition to the abundant astronomical molecule SiS. [ABSTRACT FROM AUTHOR]

By means of Fabry-Pérot Fourier transform microwave spectroscopy, the rotational spectrum of protonated sulfur dioxide in two distinct isomeric forms, a cis- and a trans-geometry, is reported. The search for both isomers was based on theoretical structures obtained at the CCSD(T)/cc-pwCVQZ level of theory corrected for zero-point vibrational effects. At a similarly high level of theory, the cis-isomer is calculated to be the global minimum on the potential energy surface, but the trans-isomer is predicted to lie only a few kcal/mol higher in energy. A total of seven lines, including a- and b-type transitions, has been observed for both isomers, and precise rotational constants have been derived. Because sulfur dioxide, SO2, is a widespread and very abundant astronomical species, and because it possesses a large proton affinity, HOSO+ is an excellent candidate for radioastronomical detection. [ABSTRACT FROM AUTHOR]

Isofulminic acid, HONC, the most energetic stable isomer of isocyanic acid HNCO, higher in energy by 84 kcal/mol, has been detected spectroscopically by rotational spectroscopy supported by coupled cluster electronic structure calculations. The fundamental rotational transitions of the normal, carbon-13, oxygen-18, and deuterium isotopic species have been detected in the centimeter band in a molecular beam by Fourier transform microwave spectroscopy, and rotational constants and nitrogen and deuterium quadrupole coupling constants have been derived. The measured constants agree well with those predicted by ab initio calculations. A number of other electronic and spectroscopic parameters of isofulminic acid, including the dipole moment, vibrational frequencies, infrared intensities, and centrifugal distortion constants have been calculated at a high level of theory. Isofulminic acid is a good candidate for astronomical detection with radio telescopes because it is highly polar and its more stable isomers (HNCO, HOCN, and HCNO) have all been identified in space. [ABSTRACT FROM AUTHOR]

The a- and b-type rotational transitions of the weakly bound complexes formed by molecular hydrogen and OCS, para-H2–OCS, ortho-H2–OCS, HD–OCS, para-D2–OCS, and ortho-D2–OCS, have been measured by Fourier transform microwave spectroscopy. All five species have ground rotational states with total rotational angular momentum J=0, regardless of whether the hydrogen rotational angular momentum is j=0 as in para-H2, ortho-D2, and HD or j=1 as in ortho-H2 and para-D2. This indicates quenching of the hydrogen angular momentum for the ortho-H2 and para-D2 species by the anisotropy of the intermolecular potential. The ground states of these complexes are slightly asymmetric prolate tops, with the hydrogen center of mass located on the side of the OCS, giving a planar T-shaped molecular geometry. The hydrogen spatial distribution is spherical in the three j=0 species, while it is bilobal and oriented nearly parallel to the OCS in the ground state of the two j=1 species. The j=1 species show strong Coriolis coupling with unobserved low-lying excited states. The abundance of para-H2–OCS relative to ortho-H2–OCS increases exponentially with decreasing normal H2 component in H2/He gas mixtures, making the observation of para-H2–OCS in the presence of the more strongly bound ortho-H2–OCS dependent on using lower concentrations of H2. The determined rotational constants are A=22 401.889(4) MHz, B=5993.774(2) MHz, and C=4602.038(2) MHz for para-H2–OCS; A=22 942.218(6) MHz, B=5675.156(7) MHz, and C=4542.960(7) MHz for ortho-H2–OCS; A=15 970.010(3) MHz, B=5847.595(1) MHz, and C=4177.699(1) MHz for HD–OCS; A=12 829.2875(9) MHz, B=5671.3573(7) MHz, and C=3846.7041(6) MHz for ortho-D2–OCS; and A=13 046.800(3) MHz, B=5454.612(2) MHz, and C=3834.590(2) MHz for para-D2–OCS. [ABSTRACT FROM AUTHOR]

The rotational spectra of five weakly bonded hydrogen-OCS complexes (paraH2, orthoH2, HD, orthoD2, and paraD2) are measured. Hyperfine structure is resolved and analyzed in all except the complex with paraH2, where I=0. For the two j=1 species, orthoH2-OCS and paraD2-OCS, nuclear hyperfine coupling constants are found to be da=21.2(2) and 8.4(2) kHz, respectively, indicative of nearly free uniaxial rotation of the hydrogen around the b-inertial axis. Similar analyses for HD-OCS and orthoD2-OCS yield the quadrupole coupling constants eqQa=16(2) and 30(2) kHz, respectively, showing that the internal rotational motions of HD and orthoD2 in the complex are slightly hindered producing a small nonspherical distribution. For orthoD2-OCS, the observed hyperfine structure indicates that the nuclear spin states I=0 and 2 are strongly coupled in the rotation of the complex. [ABSTRACT FROM AUTHOR]

Vibrational excitation and relaxation of five linear polyatomic molecules, OCS, OC3S, HC3N, HC5N, and SiC2S, have been studied by Fourier transform microwave spectroscopy in a supersonic expansion after the application of a low-current dc electric discharge. For each chain, the populations in bending and stretching modes have been characterized as a function of the applied discharge current; for stable OCS and HC3N, vibrational populations were studied as well in the absence of a discharge. With no discharge present the derived vibrational temperatures are slightly below T, the temperature of the gas before the supersonic expansion (i.e., 300 K). In the presence of the discharge, vibrational excitation occurs via inelastic collisions with the electrons and the vibrational temperatures rise as the applied current increases. Global vibrational relaxation is governed by rapid vibration–vibration (VV) energy transfer and slow vibration–translation (VT) energy transfer. The latter process is rate-determining and depends primarily on the wave number of the vibration. Vibrational modes with wave numbers near and below kT/hc (where T=300 K and kT/hc∼210 cm-1) are efficiently cooled by VT transfer because a sufficient number of collisions occur in the initial stages of the supersonic expansion. Vibrational modes with wave numbers around 450 cm-1 appear to be inefficiently cooled in the molecular beam; at these energies VV and VT rates are probably comparable. For high-frequency vibrations, VV energy transfer dominates. For the longer chains OC3S and HC5N, higher-lying modes are generally not detectable and vibrational temperatures of most lower-lying modes were found to be lower than those of OCS and HC3N, suggesting that as the size of the molecules increases, intermode VV transfer becomes more efficient, plausibly due to the higher density of vibrational levels. New high resolution spectroscopic data have been obtained for several vibrationally excited states of OC3S, HC3N, and HC5N. Rotational lines of the 13C and 15N isotopic species of HC5N have been measured, yielding improved rotational and centrifugal distortion constants; 14N nitrogen quadrupole coupling constants for the isotopic species of HC5N with 13C have been determined for the first time. [ABSTRACT FROM AUTHOR]

Fourier transform microwave spectroscopy has been used to investigate vibrational excitation and relaxation of diatomic molecules produced by an electric discharge in the throat of a supersonic nozzle. Rotational transitions of SO, SiO, and SiS, in vibrational states up to v=33 for [sup 32]S[sup 16]O, v=45 for [sup 28]Si[sup 16]O, and v=51 for [sup 28]Si[sup 32]S in their ground electronic states have been detected. The isotopic species [sup 33]S[sup 16]O, [sup 34]S[sup 16]O, [sup 29]Si[sup 16]O, [sup 28]Si[sup 18]O, [sup 29]Si[sup 32]S, and [sup 28]Si[sup 34]S have also been observed in highly excited vibrational states. Microwave transitions include up to v=22 for the second lowest excited electronic state b [sup 1]Σ[sup +] of SO (∼10 510 cm-1 above ground) have also been detected. Effective vibrational temperatures have been derived for each species, and a general model is proposed to qualitatively explain the observations. Vibrational excitation is caused by inelastic collisions with the hot electrons produced in the discharge. The subsequent vibrational populations are largely determined by vibration–vibration energy transfer via molecule–molecule binary collisions. Two regions can be inferred from the data: one characterized by a temperature of around 1000 K and a second region with a temperature of several thousand degrees Kelvin. Improved Dunham coefficients and correction terms for the breakdown of the Born–Oppenheimer approximation have been determined for b [sup 1]Σ[sup +] SO, X [sup 1]Σ[sup +] SiO, and X [sup 1]Σ[sup +] SiS. Nuclear spin-rotation hyperfine structure for the [sup 29]Si isotopic species of SiO and SiS has been observed in all highly excited vibrational states. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

On the basis of extensive coupled cluster calculations, the rotational spectra of the linear silicon- and sulfur-containing carbon chains SiC[sub 2n] S (n = 1 -3) in their singlet electronic ground state and SiC[sub 3]S in its triplet electronic ground state have been detected and characterized by means of molecular beam Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined to high accuracy as well as the spin-spin coupling constant for triplet SiC[sub 3] S. In addition, the [sup 29]Si, [sup 34]S, and both [sup 13]C isotopic species of SiC[sub 2]S have been detected, allowing the determination of both an effective r[sub 0] structure, as well as a mixed experimental-theoretical structure resulting from the combination of the measured rotational constants with the vibrationrotation coupling constants calculated ab initio. Several rotational satellite lines have also been observed for SiC[sub 2]S and, on the basis of their predicted vibration-rotation and l-type doubling constants, were assigned to the two highest-frequency stretching modes υ[sub 1] and υ[sub 2], and to a progression in the second lowest-frequency bending mode υ 4 up to 3 υ 4. Equilibrium structures and various spectroscopic properties are predicted for all SiC[sub n]S species with n = 1 - 8. [ABSTRACT FROM AUTHOR]

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Rotational transitions for omicron-benzyne were measured with a pulsed-beam, Fourier transform microwave spectrometer for all unique, singly substituted (super 13)C and single-D isotopomers. The new data combined with previous data for the normal isotopomer, provide a complete set of structural parameters for this molecule and the r(sub s) substitution coordinates and the coordinates from a least-squares fit are reported.

The rotational spectrum of thiozene that is S3 by Fourier transform microwave (FTM) spectroscopy of a molecular beam is detected. It is analyzed that the symmetry of S3 can detect its structure with the two geometrical parameters.

Following the recent discovery of T-shaped GeC2, rotational spectra of three larger Ge carbides, linear GeC4, GeC5, and GeC6 have been observed using chirped pulse and cavity Fourier transform microwave spectroscopy and a laser ablation molecule source, guided by new high-level quantum chemical calculations of their molecular structure. Like their isovalent Si-bearing counterparts, Ge carbides with an even number of carbon atoms beyond GeC2 are predicted to possess 1Σ ground electronic states, while odd-numbered carbon chains are generally 3Σ; all are predicted to be highly polar. For the three new molecules detected in this work, rotational lines of four of the five naturally occurring Ge isotopic variants have been observed between 6 and 22 GHz. Combining these measurements with ab initio force fields, the Ge–C bond lengths have been determined to high precision: the derived values of 1.776 Å for GeC4, 1.818 Å for GeC5, and 1.782 Å for GeC6 indicate a double bond between these two atoms. Somewhat surprisingly, the spectrum of GeC5 very closely resembles that of a 1Σ molecule, implying a spin–spin coupling constant λ in excess of 770 GHz for this radical, a likely consequence of the large spin–orbit constant of atomic Ge (∼1000 cm−1). A systematic comparison between the production of SiCn and GeCn chains by laser ablation has also been undertaken. The present work suggests that other large metal-bearing molecules may be amenable to detection by similar means. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols are large clusters of molecules and particulate matter that profoundly affect the Earth's radiation budget and climate. Gas-phase oxidation of volatile organic compounds is thought to play a key role in nucleation and aerosol growth, but remains poorly understood. One reaction proposed to trigger formation of condensable, low volatility organic compounds is that between Criegee intermediates and carboxylic acids to yield hydroperoxide esters. Here we isolate in high yield the simplest hydroperoxide ester, hydroperoxymethyl formate (HOOCH2OCHO), as a secondary product in the ozonolysis of ethylene, and establish by rotational spectroscopy that this ester adopts a nearly-rigid cyclic structure owing to a strong hydrogen bond between the peroxy hydrogen and carbonyl oxygen. Subsequent detection of this ester in the ozonolysis of propylene and isoprene suggests that terminal alkenes readily undergo specific types of second-order oxidation reactions that have been implicated in the formation of atmospheric aerosols. [ABSTRACT FROM AUTHOR]

We report the gas-phase detection and spectroscopic characterisation of ethynethiol (), a metastable isomer of thioketene () using a combination of Fourier-transform microwave and submillimetre-wave spectroscopies. Several a-type transitions of the normal species were initially detected below 40 GHz using a supersonic expansion-electrical discharge source, and subsequent measurement of higher-frequency, b-type lines using double resonance provided accurate predictions in the submillimetre region. With these, searches using a millimetre-wave absorption spectrometer equipped with a radio frequency discharge source were conducted in the range 280–660 GHz, ultimately yielding nearly 100 transitions up to and. From the combined data set, all three rotational constants and centrifugal distortion terms up to the sextic order were determined to high accuracy, providing a reliable set of frequency predictions to the lower end of the THz band. Isotopic substitution has enabled both a determination of the molecular structure of HCCSH and, by inference, its formation pathway in our nozzle discharge source via the bimolecular radical-radical recombination reaction , which is calculated to be highly exothermic (−477 kJ/mol) using the HEAT345(Q) thermochemical scheme. [ABSTRACT FROM AUTHOR]

The article focuses on the role of universities in society. Topics discussed include disciplinary and the fiscal practices of higher education; classic work of Philip Selznick on link between higher education and social values; and the priority of a deeper understanding of human values as a control over technological development.

Context. Protonated molecular species have been proven to be abundant in the interstellar gas. This class of molecules is also pivotal for the determination of important physical parameters for the evolution of the interstellar medium (e.g. gas ionisation fraction) or as tracers of non-polar species which are not directly observable. The identification of these molecular species through radioastronomical observations is directly linked to precise laboratory spectral characterisation. Aims. The goal of the present work is to extend the laboratory measurements of the pure rotational spectrum of the ground electronic state of protonated carbonyl sulfide (HSCO+) and its deuterium substituted isotopomer (DSCO+). At the same time, we show how implementing different laboratory techniques allows for the determination of different spectroscopical properties of asymmetric-top protonated species. Methods. Three different high-resolution experiments were used in conjunction to detect for the first time the b-type rotational spectrum of HSCO+, and to extend, well into the sub-millimetre region, the a-type spectrum of the same molecular species and DSCO+. The electronic ground-state of both ions was investigated in the 273–405 GHz frequency range, allowing for the detection of 60 and 50 new rotational transitions for HSCO+ and DSCO+, respectively. Results. The combination of our new measurements with the three rotational transitions previously observed in the microwave region permits the rest frequencies of the most astronomically relevant transitions to be predicted to better than 100 kHz for both HSCO+ and DSCO+ up to 500 GHz, equivalent to better than 60 m s−1 in terms of equivalent radial velocity. Conclusions. The present work illustrates the importance of using different laboratory techniques to spectroscopically characterise a protonated species at high frequency. Each instrument addressed a complementary part of the same spectroscopic challenge, demonstrating the potential of such an approach for future studies of similar reactive species. [ABSTRACT FROM AUTHOR]

Several variants of the one-laser, two-color technique of sideband optical–optical double resonance Zeeman (SOODRZ) spectroscopy, which enables Zeeman and hyperfine splittings to be measured at sub-Doppler resolution, are described; a detailed theory of the line shape and signal-to-noise ratio for each variant is also presented. In the single-frequency variant of SOODRZ spectroscopy, radio frequency sidebands are imposed onto a single-frequency continuous wave laser beam to determine energy splittings between pairs of closely spaced levels. Each pair of closely spaced levels is coupled to a third isolated level by optical transitions and is tuned into resonance by the Zeeman effect. A theoretical treatment of the SOODRZ effect is presented here. It is shown that both the real and imaginary contributions to the complex third-order optical susceptibility tensor χ(3) can be observed and that the SOODRZ signal originates from a cross term between the amplitude of the unperturbed frequency-modulated beam of the laser and the nonlinear signal amplitude Re{EL*·ENL}. The SOODRZ signal is directly proportional to ΔNμ4MI20 (where M is the modulation index), rather than (ΔN)2, μ8, and I30 as in degenerate four-wave mixing and other nonlinear spectroscopies, which means the detection sensitivity of SOODRZ spectroscopy is considerably higher for low laser intensities and at lower number densities.Moreover, the linewidth of the sub-Doppler feature is independent of the both the Doppler width of the optical transition and the natural width of the common linked level and, hence, is immune from the effects such as upper state predissociation. Two different types of modulators, acousto-optic and electro-optic, can be used in the single-frequency variant of SOODRZ spectroscopy. The unique features of SOODRZ schemes incorporating both types of modulators are described. SOODRZ spectroscopy can also be performed with a multimode broadband... [ABSTRACT FROM AUTHOR]

The technique of frequency-modulation enhanced magnetic rotation spectroscopy (FM-MRS) is applied here to the study of the electronic spectra of gas-phase transition metal hydrides and deuterides. Experimental FM-MR results for several bands of PdH, PdD, NiH, and CuH are presented. In the case of PdH, an Ω=0.5–XΩ=0.5 band at 4371 Å has been observed and assigned. Prior to this work, although several bands of PdD had been reported previously, no electronic transitions of PdH had been assigned. All of the PdH, PdD, and NiH bands studied in the 4200–4600 Å wavelength region are strongly predissociated, and in the case of PdH and PdD, strongly and multiply perturbed as well. [ABSTRACT FROM AUTHOR]

The technique of frequency-modulation enhanced magnetic rotation spectroscopy (FM-MRS) is described. An experimental comparison between FM-MRS, frequency-modulation, and magnetic rotation spectroscopies clearly demonstrates that the double null absorption-based FM-MR technique is more sensitive than either FM or MRS separately. The theoretical basis for this sensitivity enhancement can be attributed to a 1/θ (where θ is the small uncrossing angle between two nearly crossed polarizers) improvement in the sensitivity of the combined FM-MR technique relative to that of standard FM spectroscopy. The sensitivity improvement of FM-MRS relative to MRS is even better than that for FM spectroscopy. In practical terms, this enhancement can improve the experimentally achievable sensitivity of FM and magnetic rotation spectroscopies by factors of O(101) to O(102) and O(102) to O(104), respectively, levels that approach the theoretical quantum noise limit. In addition, because FM-MRS is based on the Zeeman effect, Zeeman information is encoded into FM-MR line profiles in the form of relative phase labels and line shapes. The relative phases and line shapes of rotational lines can be used to group features by rotational branch and to differentiate between magnetically active (Λ≠0, Σ≠0) and inactive (Λ=0, Σ=0) features. The theory of FM-MRS, including a discussion of line shapes and a sensitivity analysis, is reviewed here; applications of the FM-MR technique are presented separately in the following paper. [ABSTRACT FROM AUTHOR]

The application of magnetic rotation spectroscopy (MRS) to the electronic spectra of gas phase NiH and CeF is examined. Experimental results for both MRS and laser excitation spectroscopy are presented for the NiH B 2Δ5/2–X 2Δ5/2 (1,0) and 2[uppercase_phi_synonym]7/2–X 2Δ5/2 (0,0) bands. A comparison between these two techniques clearly illustrates the ability of MRS to simplify and presort spectra. The power of MRS originates from its specificity for low-J, ΔΩ=ΔJ transitions and its ability, based on the sign and magnitude of the MRS effect, to partially presort rotational branches. A simple theoretical explanation of the MRS results, based on the structure of the underlying Zeeman pattern, is presented. Also, the extension of MRS to the more complicated and congested spectrum of CeF is presented. Using MRS, a previously unassigned CeF band, near 568 nm, has been definitively assigned as Ω’=4.5←Ω‘=3.5. [ABSTRACT FROM AUTHOR]

Uses the sideband optical-optical double resonance Zeeman effect spectroscopy to study the electronic spectrum of the gas-phase platinum-hydrogen compound. Analysis of the sub-Doppler Zeeman spectrum of each feature using a systematic quasi-two-dimensional approach; Radio frequency magnetic resonances.

Applies the sideband optical-optical double resonance Zeeman effect spectroscopy to study transition metal hydrides. Resolution of the extremely small ground state photon hyperfine splittings; Record of the sub-dopper spectra; Deviation of the g values in each state from the nominal Hund's coupling case.

The equilibrium structure for the ground state of the HNCN radical is calculated at the levels of the self-consistent field theory (SCF), the second-order Mo\ller–Plesset perturbation approximation (MP2), and the full single and double excitation coupled cluster theory including all connected triples in a noniterative manner [CCSD(T)], using various extended basis sets starting from 6–311 G(d,p). At the CCSD(T) level, the outer C–N bond is more than 0.1 Å shorter than the inner one and the N–C–N group departs from linearity by 6°. The total N–C–N length is in good agreement with the experimental value [Herzberg and Warsop, Can. J. Phys. 41, 286 (1963)], however, the H–N–C angle is about 6° smaller. The N–H bond is very close to a normal N–H bond but is about 0.2 Å smaller than the experimental estimate. Except for the smaller H–N–C angle, the geometrical parameters for HNCN closely parallel those for the triplet HCCN molecule. The dipole moment, harmonic frequencies, electric quadrupole, and Fermi contact coupling constants of HNCN are also calculated. The calculated harmonic frequencies confirm the preliminary assignments of Wu, Hall, and Sears [J. Chem. Soc. Faraday Trans. 89, 615 (1993)]. The quadrupole coupling constants for the inner and outer N atoms are comparable, implying a complex pattern of hyperfine split components in the lowest rotational transitions. The present calculation may thus serve as a useful guide for the interpretation of the rotational spectrum. [ABSTRACT FROM AUTHOR]