Mm-wave Spectra Research Articles

Compact and wideband nanoacoustic pass-band filters for future 5G and 6G cellular radios

Over recent years, the surge in mobile communication has deepened global connectivity. With escalating demands for faster data rates, the push for higher carrier frequencies intensifies. The 7–20 GHz range, located between the 5G sub-6 GHz and the mm-wave spectra, provides an excellent trade-off between network capacity and coverage, and constitutes a yet-to-be-explored range for 5G and 6G applications. This work proposes a technological platform able to deliver CMOS-compatible, on-chip multi-frequency, low-loss, wide-band, and compact filters for cellular radios operating in this range by leveraging the micro-to-nano scaling of acoustic electromechanical resonators. The results showcase the first-ever demonstrated low insertion loss bank of 7 nanoacoustic passband filters in the X-band. Most of the filters showcase fractional bandwidths above 3% and sub-dB loss per stage in an extremely compact form factor, enabling the manufacturing of filters and duplexers for the next generation of mobile handsets operating in the X-band and beyond.

Millimeter-Wave Spectroscopy of Methylfuran Isomers: Local vs. Global Treatments of the Internal Rotation.

Methylfurans are methylated aromatic heterocyclic volatile organic compounds and primary or secondary pollutants in the atmosphere due to their capability to form secondary organic aerosols in presence of atmospheric oxidants. There is therefore a significant interest to monitor these molecules in the gas phase. High resolution spectroscopic studies of methylated furan compounds are generally limited to pure rotational spectroscopy in the vibrational ground state. This lack of results might be explained by the difficulties arisen from the internal rotation of the methyl group inducing non-trivial patterns in the rotational spectra. In this study, we discuss the benefits to assign the mm-wave rotational-torsional spectra of methylfuran with the global approach of the BELGI-C code compared to local approaches such as XIAM and ERHAM. The global approach reproduces the observed rotational lines of 2-methylfuran and 3-methylfuran in the mm-wave region at the experimental accuracy for the ground v and the first torsional v states with a unique set of molecular parameters. In addition, the and parameters describing the internal rotation potential barrier may be determined with a high degree of accuracy with the global approach. Finally, a discussion with other heterocyclic compounds enables the study of the influence of the electronic environment on the hindered rotation of the methyl group.

Radar Imaging Based on IEEE 802.11ad Waveform in V2I Communications

Since most of vehicular radar systems are already exploiting millimeter-wave (mmWave) spectra, it would become much more feasible to implement a joint radar and communication system by extending communication frequencies into the mmWave band. In this paper, an IEEE 802.11ad waveform-based radar imaging technique is proposed for vehicular settings. A roadside unit (RSU) transmits the IEEE 802.11ad waveform to a vehicle for communications while the RSU also listens to the echoes of transmitted waveform to perform inverse synthetic aperture radar (ISAR) imaging. To obtain high-resolution images of the vehicle, the RSU needs to accurately estimate round-trip delays, Doppler shifts, and velocity of vehicle. The proposed ISAR imaging first estimates the round-trip delays using a good correlation property of Golay complementary sequences in the IEEE 802.11ad preamble. The Doppler shifts are then obtained using least square estimation from the echo signals and refined to compensate phase wrapping caused by phase rotation. The velocity of vehicle is determined using an equation of motion and the estimated Doppler shifts. Simulation results verify that the proposed technique is able to form high-resolution ISAR images from point scatterer models of realistic vehicular settings with different viewpoints. The proposed ISAR imaging technique can be used for various vehicular applications, e.g., traffic condition analyses or advanced collision warning systems.

Tracing the Milky Way's Vestigial Nuclear Jet

MeerKAT radio continuum and XMM-Newton X-ray images have recently revealed a spectacular bipolar channel at the Galactic Center that spans several degrees ($\sim$0.5 kpc). An intermittent jet likely formed this channel and is consistent with earlier evidence of a sustained, Seyfert-level outburst fueled by black-hole accretion onto SgA* several Myr ago. Therefore, to trace an intermittent jet that perhaps penetrated, deflected, and percolated along multiple paths through the interstellar medium, relevant interactions are identified and quantified in archival X-ray images, Hubble Space Telescope Paschen-$\alpha$ images and ALMA mm-wave spectra, and new SOAR telescope IR spectra. Hydrodynamical simulations are used to show how a currently weak jet can explain these structures and inflate the ROSAT/eROSITA X-ray and Fermi $\gamma$-ray bubbles that extend $\pm$60 deg from the Galactic plane. Thus, our Galactic outflow has features in common with energetic, jet-driven structures in the prototypical Seyfert galaxy NGC 1068.

3D Spatial Reuse of Multi-Millimeter-Wave Spectra by Ultra-Dense In-Building Small Cells for Spectral and Energy Efficiencies of Future 6G Mobile Networks

The sixth-generation (6G) mobile networks are expected to operate at a higher frequency to achieve a wider bandwidth and to enhance the frequency reuse efficiency for improved spectrum utilization. In this regard, three-dimensional (3D) spatial reuse of millimeter-wave (mmWave) spectra by in-building small cells is considered an effective technique. In contrast to previous works exploiting microwave spectra, in this paper, we present a technique for the 3D spatial reuse of 28 and 60 GHz mmWave spectra by in-building small cells, each enabled with dual transceivers operating at 28 and 60 GHz bands, to enhance frequency reuse efficiency and achieve the expected spectral efficiency (SE) and energy efficiency (EE) requirements for 6G mobile networks. In doing so, we first present an analytical model for the 28 GHz mmWave spectrum to characterize co-channel interference (CCI) and deduce a minimum distance between co-channel small cells at both intra- and inter-floor levels in a multistory building. Using minimum distances at both intra- and inter-floor levels, we find the optimal 3D cluster size for small cells and define the corresponding 3D spatial reuse factor, such that the entire 28 and 60 GHz spectra can be reused by each 3D cluster in each building. Considering a system architecture where outdoor macrocells and picocells operate in the 2 GHz microwave spectrum, we derive system-level average capacity, SE, and EE values, as well as develop an algorithm for the proposed technique. With extensive numerical and simulation results, we show the impacts of 3D spatial reuse of multi-mmWave spectra by small cells in each building and the number of buildings per macrocell on the average SE and EE performances. Finally, it is shown that the proposed technique can satisfy the expected average SE and EE requirements for 6G mobile networks.

Low-Loss Impedance-Matched Sub-25-μm Vias in 3-D Millimeter-Wave Packages

This article presents, for the first time, low-loss small microvias in build-up layers for the next-generation highdensity high-performance fifth-generation (5G) millimeter-wave (mm-wave) antenna-integrated packages. As the operating frequency increases, the signal losses in antenna packages become more critical and need to be mitigated to obtain desired performance in beamforming and massive multi-input multioutput. As electrical wavelengths in mm-wave spectra are short, the signal losses caused by microvias dominate the loss budget. To minimize the signal losses and identify the required microvia diameter in build-up layers, this article first focuses on the modeling of small microvias for impedance matching. Based on the models and simulated characteristic impedance, test vehicles with daisy chains are fabricated in build-up layers on a core package substrate. Ultraviolet (UV) laser is utilized to drill microvias, and targeted microvia diameters are obtained through a semiadditive patterning process. High-frequency measurements are also performed to correlate with the models and simulated results in the 28-GHz band. The characterization results exhibit good model-to-hardware correlation and indicate that small microvias (20 μm) provide impedance closer to 50 Ω compared with the larger microvias. This matched microvia impedance lowers reflection and insertion loss, resulting in a 10% reduction in the signal losses caused by microvias in the 5G New-Radio n257 band around 28 GHz.

Physical Layer Security for Visible Light Communication Systems: A Survey

Due to the dramatic increase in high data rate services and in order to meet the demands of the fifth-generation (5G) networks, researchers from both academia and industry are exploring advanced transmission techniques, new network architectures and new frequency spectrum such as the visible light and the millimeter wave (mmWave) spectra. Visible light communication (VLC) particularly is an emerging technology that has been introduced as a promising solution for 5G and beyond, owing to the large unexploited spectrum, which translates to significantly high data rates. Although VLC systems are more immune against interference and less susceptible to security vulnerabilities since light does not penetrate through walls, security issues arise naturally in VLC channels due to their open and broadcasting nature, compared to fiber-optic systems. In addition, since VLC is considered to be an enabling technology for 5G, and security is one of the 5G fundamental requirements, security issues should be carefully addressed and resolved in the VLC context. On the other hand, due to the success of physical layer security (PLS) in improving the security of radio-frequency (RF) wireless networks, extending such PLS techniques to VLC systems has been of great interest. Only two survey papers on security in VLC have been published in the literature. However, a comparative and unified survey on PLS for VLC from information theoretic and signal processing point of views is still missing. This paper covers almost all aspects of PLS for VLC, including different channel models, input distributions, network configurations, precoding/signaling strategies, and secrecy capacity and information rates. Furthermore, we propose a number of timely and open research directions for PLS-VLC systems, including the application of measurement-based indoor and outdoor channel models, incorporating user mobility and device orientation into the channel model, and combining VLC and RF systems to realize the potential of such technologies.

The pure rotational spectrum of the ScO (X2Σ+) radical

The rotational spectrum of ScO (X2Σ+) has been measured in the gas phase in the frequency range 30–493GHz using a combination of Fourier transform microwave/millimeter-wave (FTM/mmW) and submillimeter direct absorption methods. This work is the first pure rotational study of this radical. Both the ground vibrational and v=1 states were observed. ScO was created from the reaction of metal vapor, produced either by a laser ablation source or a Broida-type oven, and N2O, in the former case heavily diluted in argon. Extensive hyperfine structure was observed in the FTM/mmW data, although the spin-rotation splitting was found to be small (∼3MHz). In the mm-wave spectra, however, the fine and hyperfine structure was blended together, resulting in broad, single lines for a given transition N+1←N. The data were analyzed in a combined fit using the very accurate hyperfine measurements of Childs and Steimle (1988), employing a Hund’s case b Hamiltonian, and an improved set of rotational and centrifugal distortion constants were determined. These measurements improve the accuracy of predicted frequencies for astronomical searches by 14–18MHz, or 16–20km/s, in the 1mm region – a difference of half to a full linewidth for certain interstellar sources. This work also demonstrates the capabilities of the FTM/mmW spectrometer at 61GHz.

ThePlanck–ATCA Co-eval Observations project: analysis of radio source properties between 5 and 217 GHz

The Planck–ATCA Co-eval Observations (PACO) project has yielded observations of 464 sources with the Australia Telescope Compact Array (ATCA) between 4.5 and 40 GHz. The main purpose of the project was to investigate the spectral properties of mm-selected radio sources at frequencies below and overlapping with the ESA's Planck satellite frequency bands, minimizing the variability effects by observing almost simultaneously with the first two Planck all-sky surveys. In this paper we present the whole catalogue of observations in total intensity. By comparing PACO with the various measures of Planck Catalog of Compact Sources (PCCS) flux densities we found the best consistency with the PCCS ‘detection pipeline’ photometry (DETFLUX) that we used to investigate the spectral properties of sources from 5 to 217 GHz. Of our sources, 91 per cent have remarkably smooth spectrum, well described by a double power-law over the full range. This suggests a single emitting region, at variance with the notion that ‘flat’ spectra result from the superposition of the emissions from different compact regions, self-absorbed up to different frequencies. Most of the objects show a spectral steepening above ≃30 GHz, consistent with synchrotron emission becoming optically thin. Thus, the classical dichotomy between flat-spectrum/compact and steep-spectrum/extended radio sources, well established at cm wavelengths, breaks down at mm wavelengths. The mm-wave spectra do not show indications of the spectral break expected as the effect of ‘electron ageing’, suggesting young source ages.

Trends in alkali metal hydrosulfides: A combined Fourier transform microwave/millimeter-wave spectroscopic study of KSH ($\tilde X^1 A^\prime $X̃1A′)

The pure rotational spectrum of KSH (X(1)A') has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) techniques. This work is the first gas-phase experimental study of this molecule and includes spectroscopy of KSD as well. In the millimeter-wave system, KSH was synthesized in a DC discharge from a mixture of potassium vapor, H2S, and argon; a discharge-assisted laser ablation source, coupled with a supersonic jet expansion, was used to create the species in the FTMW instrument. Five and three rotational transitions in the range 3-57 GHz were recorded with the FTMW experiment for KSH and KSD, respectively, in the K(a) = 0 component; in these data, potassium quadrupole hyperfine structure was observed. Five to six transitions with K(a) = 0-5 were measured in the mm-wave region (260-300 GHz) for the two species. The presence of multiple asymmetry components in the mm-wave spectra indicates that KSH has a bent geometry, in analogy to other alkali hydrosulfides. The data were analyzed with an S-reduced asymmetric top Hamiltonian, and rotational, centrifugal distortion, and potassium electric quadrupole coupling constants were determined for both isotopolgues. The r0 geometry for KSH was calculated to be r(S-H) = 1.357(1) Å, r(K-S) = 2.806(1) Å, and θ(M-S-H) (°) = 95.0 (1). FTMW measurements were also carried out on LiSH and NaSH; metal electric quadrupole coupling constants were determined for comparison with KSH. In addition, ab initio computations of the structures and vibrational frequencies at the CCSD(T)/6-311++G(3df,2pd) and CCSD(T)/aug-cc-pVTZ levels of theory were performed for LiSH, NaSH, and KSH. Overall, experimental and computational data suggest that the metal-ligand bonding in KSH is a combination of electrostatic and covalent forces.

Rotational structure of the five lowest frequency fundamental vibrational states of dimethylsulfoxide

We report on the successful extended analysis of the high-frequency (200–700GHz) part of the gas phase (sub)mm-wave spectra of dimethylsulfoxide (DMSO). The spectrum was recorded at 100kHz resolution using a solid state subTHz spectrometer. The five lowest energy fundamental vibrational states of DMSO with frequencies below 400cm−1 were observed as sidebands along with the main 0←0 band. Neglecting the internal rotation of methyls, our rotational Hamiltonian reproduced the spectrum to the subMHz accuracy. We have found that the asymmetric bending state ν23 is the only low frequency fundamental vibrational state with the “anomalous” rotational structure uncovered in Cuisset et al. [1]. dmsomw 2013-09-04 15:03 © 2013 Elsevier

EXPERIMENTAL CONDITIONS FOR THE EXCITATION OF THIN DISK WHISPERING-GALLERY-MODE RESONATORS

Measurements of mm-wave excitation spectra of highorder whispering gallery modes in free-space cylindrical disk resonators as functions of resonator thickness have been made. Resonators in the form of tight stacks of thin dielectric disks excited via dielectric waveguides have been used in the experiment. Experimental conditions for the excitation of thin-disk resonators have been found. A simple approach for the modeling of resonator spectra and recovery of dielectric parameters has been proposed.

Water vapor variations in the Venus mesosphere from microwave spectra

Mm-wave spectra of HDO in the Venus mesosphere (65–100 km) were obtained over the period March 1998 to June 2004. Each spectrum is a measurement of the hemispheric-average H 2O vapor mixing ratio in the Venus mesosphere. Observations were conducted for wide ranges of Venus solar elongations (46° W to 47° E), and fractional disk illuminations ( f = 0 % to 99%), yielding water vapor abundances on 17 dates and over a full range of local solar time (LST) at the sub-Earth point on Venus. Our mesopheric H 2O values are more numerous and far more precise than the earliest mm-derived H 2O measurements [Encrenaz, Th., Lellouch, E., Paubert, G., Gulkis, S., 1991. First detection of HDO in the atmosphere of Venus at radio wavelengths: An estimate of the H 2O vertical distribution. Astron. Astrophys. 246, L63–L66; Encrenaz, Th., Lellouch, E., Cernicharo, J., Paubert, G., Gulkis, S., Spilker, T., 1995. The thermal profile and water abundance in the Venus mesosphere from H 2O and HDO millimeter observations. Icarus 117, 162–172], allowing an analysis of variability that was previously impossible. Measured 65–100 km H 2O ranged from 0.0 ± 0.06 to 3.5 ± 0.3 ppmv , with significantly different variability than found in previous infrared (lower altitude, cloudtop) studies. Strong global variability on a 1–2 month timescale is clear and unambiguous. A limited number of excellent s/n measurements tentatively indicate the 1–2 month variability manifests most rapidly as change in the lower mesosphere, and more slowly as change in the upper mesosphere. Neither long term (1998–2004) nor diurnal variability in 65–100 km H 2O is evident. While six-year and/or diurnal variabilities are not ruled out, they are weaker than the 1–2 month timescale variation. These conclusions are supported by initial (2004) sub-mm measurements.

The ∠ICI Bending Satellites in the Millimeter-Wave Rotational Spectra of CH2I2 and CD2I2

Rotational transitions in the first four excited states of the low-frequency ∠ICI bending mode, ν4, have been assigned in the mm-wave rotational spectra of CH2I2 and of CD2I2. Measurements of transition frequencies, made over the frequency region 167–326 GHz and for J" up to 190, allowed determination of sextic level spectroscopic constants for all states. The changes in spectroscopic constants with vibrational excitation show very small anharmonicity, in spite of the very low frequency of this mode (121 cm−1). Vibrational excitation affects the moments of inertia in such a way that the planar moment Pb, about the plane perpendicular to both ∠ICI and ∠HCH, is practically invariant. Vibrational change in Pc, the moment along the principal axis in the HCH plane and perpendicular to the ∠HCH bisector, has been successfully reproduced with an ab initio harmonic force field so that there is no discernible vibrational change in ∠HCH on excitation of ∠ICI. Finally, the change in Pa leads to estimated vibrational change of +0.12° in the value of ∠ICI itself.

Magnetic-field-induced electronic phase transitions in semimetals in high magnetic fields

We report an experimental study of the magnetic-field-induced electronic phase transitions in semimetals (graphite and Bi) in pulsed high magnetic fields up to several hundred teslas. Far-infrared and millimetre-wave spectroscopies were employed to investigate the electric conductivity and the optical transitions between the Landau levels. In graphite a phase transition was observed in the mm-wave transmission through a specially designed strip-line system with a sample on one of the walls. Evidence of a density-wave phase transition was found in the infrared transmission at a transition field of about 30-40 T. Cyclotron resonance in very high field revealed that the n = 0 spin-up level is depopulated above a field of B = 54 T, while the n = 0 spin-down level persists under the Fermi level at least up to 200 T. In Bi, anomalous structures were observed in the strip-line mm-wave transmission spectra as well as the infrared transmission spectra, indicating a semimetal-to-semiconductor transition at around 85 T.

The Heliocentric Evolution of Key Species in the Distantly-Active Comet C/1995 O1 (Hale-Bopp)

view Abstract Citations (25) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Heliocentric Evolution of Key Species in the Distantly-Active Comet C/1995 O1 (Hale-Bopp) Womack, Maria ; Festou, M. C. ; Stern, S. Alan Abstract Comet Hale-Bopp (C/1995 01) presents the first opportunity to study physical and chemical changes in the coma of a bright, active comet at large heliocentric distances with modern millimeter-wavelength spectrometers. We obtained mm-wave spectra of CH3OH, CO, and H2CO in Hale-Bopp on 29 dates when it was beyond 4 AU. We report the first detection of CH3OH in Hale-Bopp at 5.0 AU. Additionally, we found that CO production went through three distinct phases: (i) an initial, rapid increase, (ii) quasi-saturation, and then (iii) a renewed, but less rapid increase. The abrupt renewal of the CO production rate increase took place near both the onset of H2O sublimation and the first detections of CH3OH and HCN, suggesting a causal relationship. Line shape and velocity offset information in our spectra give important clues to the production mechanisms of the three species. Linewidths were relatively narrow (0.3 km s-1) for CO and much wider (1-2 km s-1) for CH3OH and H2CO. Line profiles of CO were substantially blueshifted with respect to the comet's frame of reference by an average of 0.3 km s-1, while CH3OH and H2CO emission appeared essentially at rest with respect to the comet's frame. Based on these findings, we infer that the CO we observed was produced primarily at the nucleus in jets, rather than from an extended source, and that the majority of both the CH3OH and H2CO appear instead to be released as daughter products from the dissociation of heavier molecules. Publication: The Astronomical Journal Pub Date: December 1997 DOI: 10.1086/118687 Bibcode: 1997AJ....114.2789W Keywords: COMETS: INDIVIDUAL: HALE BOPP full text sources ADS |

Isotopic NS rotational spectra: 14N 33S and 15N 32S

The mm-wave spectra of the NS radical isotopomers 14N 33S and 15N 32S have been measured. Furthermore, new lines of the 14N 34S species have been recorded. The radicals were generated in a dc glow discharge of a mixture of N 2 and H 2S. All new lines belong to the 2Π 1 2 substates and were observed in natural abundance. The new data have been fitted simultaneously together with previously reported 14N 32S and 14N 34S lines to yield molecular constants, including the Born-Oppenheimer corrections δ 01 S and Δ 01 N and the 33S hyperfine constants d and a − (b + c) 2 .

Rotational Spectra of 14N17O and 15N18O

Abstract The mm-wave spectra of 15N18 O and 14N 17 O in both X2 Π1/2 and X2 Π3/2 states have been measured and assigned for the first time. Improved rotational and, for the first time, 17O hyperfine coupling constants have been derived from the analysis. The 14N17 O data yield parameters of the unpaired electron spatial distribution near both nuclei. Furthermore, the deviation from the Born-Oppenheimer approximation is confirmed on the basis of the rotational constants of five isotopomers. Finally, when comparing the nuclear spin-rotation constants to the ones of other molecules containing 14N or 17O nuclei, a roughly linear proportionality with the rotational constant B is found.

The microwave spectra of NSF3 in vibrationally excited states

The mm-wave spectra of 14N32SF3 in the excited vibrational states v 5 = 1 and v 6 = 1 have been recorded. Analyses of these have yielded values for the Av rotational constants and hence a better determined structure. In addition the coriolis constants ζ55 z = -0·2256 (18) and ζ66 z = 0·1569 (15) have been obtained. These have been combined with accurate measurements of the centrifugal distortion constants of the ground state, some isotopic vibrational data and ζ66 z = 0·1657 (15) for 14N34SF3 to give a good estimate of the most general valence force field.

The millimeter wave spectra of isocyanic and isothiocyanic acids

An investigation of the mm-wave rotational spectra of the very slightly asymmetric tops HNCS, DNCS, HNCO and DNCO has been carried out in the frequency range 80 000–190 000 Mc/sec. Several R-branch, a-type, transitions were observed for each molecule and the rotational constants A 0, B 0, and C 0 were determined for the four species containing the most abundant isotopes of N, C, O, or S. B 0 and C 0 were also found for HNCS 34. The centrifugal distortion constant D J was obtained for each abundant form. The constants are HNCS: A 0 = 1 483 000 ± 167 000 Mc/sec, B 0 = 5883.42 ± 0.02 Mc/sec, C 0 = 5845.62 ± 0.02 Mc/sec, D j = 1.17 ± 0.05 Kc/sec; DNCS: A 0 = 723 400 ± 25 000 Mc/sec, B 0 = 5500.51 ± 0.05 Mc/sec, C 0 = 5445.26 ± 0.05 Mc/sec, D j = 1.22 ± 0.31 Kc/sec; HNCS 34: B 0 = 5744.81 ± 0.20 Mc/sec, C 0 = 5708.73 ± 0.20 Mc/sec; HNCO: A 0 = 956 400 ± 50 000 Mc/sec, B 0 = 11 071.02 ± 0.05 Mc/sec, C 0 = 10 910.58 ± 0.05 Mc/sec, D j = 3.5 ± 0.5 Kc/sec; DNCO: A 0 = 534 500 ± 70 000 Mc/sec, B 0 = 10 313.61 ± 0.05 Mc/sec, C 0 = 10 079.67 ± 0.05 Mc/sec, D j = 2.9 ± 0.5 Kc/sec. The centrifugal distortion K-pattern is different in character for each of the four molecules. Agreement between calculation and experiment is obtained for HNCO and DNCO with the additional constants; HNCO; D JK = +837 Kc/sec, H JJK = −0.056 Kc/sec, H JKK = +2.81 Kc/sec. DNCO: D JK = −227.1 Kc/sec, H JJK = +0.15 Kc/sec, H JKK = −5.61 Kc/sec, H JJJ = 0, utilizing the expression given by Costain. This expression gives a poor fit for DNCS and no fit for HNCS, and at present no treatment has been found to fit or explain satisfactorily the K-patterns for these two molecules. An improved molecular structure has been calculated for HNCS the structural parameters being revised to r(HN) = 0.988 7 ± 0.003 A, r(NC) = 1.216 4 ± 0.007 A, r(CS) = 1.560 5 ± 0.003 A < HNC = 134°59′ ± 10′. A number of lines due to rotational transitions of vibrationally excited molecules were also observed and are assigned to the states v 5 = 1 and v 6 = 1 for HNCS and HNCO and probably, in addition, v 4 = 1 for DNCS.