L-type Doubling Research Articles

High-Temperature Line List of Phosphaethyne (HCP).

Phosphaethyne (HCP) has been detected in circumstellar envelopes; its spectroscopic line list is helpful for modeling the relevant atmospheric opacity. We present the first comprehensive line list for HCP(X1Σ+) using robust first-principles methods. The analytical potential energy surface and dipole moment surface were constructed based on 26478 ab initio points from coupled-cluster calculations, along with the considerations of core-valence electron correlation and scalar relativistic effects. The variational nuclear motion program TROVE was used to obtain the ro-vibrational energy levels, Einstein A coefficients, and so on. The J-dependent Coriolis-decoupled Hamiltonian was adopted in the variational calculations with k ≤ 20, and the linear molecule treatment was applied to consider the l-type doubling of the bending vibration. The line list contains almost 0.45 billion transitions between 1.21 million levels with rotational excitation up to J = 200. It covers the wavenumber range of 0-9000 cm-1 (wavelengths above 1.11 μm) and is suitable for temperatures up to 3000 K. The millimeter wave spectra agree well with the experiments, and the Fermi resonance between 2v2 and v3 bands has been reproduced.

High-temperature spectra of the PNO molecule based on robust first-principles methods.

The PNO molecule is an important species found in the interstellar medium, and its spectroscopic information is helpful for its detection. We present the first line list of PNO (X1Σ+) using robust first-principles methods. The analytical potential energy surface and the dipole moment surface were constructed based on 11 942 ab initio points. The variational nuclear motion calculation was implemented in TROVE to obtain the rovibrational energy levels, Einstein A coefficients and other parameters. The J-dependent Coriolis-decoupled Hamiltonian was adopted with k ≤ 15, and the l-type doubling was considered for the bending vibration of the linear molecule. The line list contained almost 5.87 billion transitions between 3.61 million levels with rotational excitation up to J = 200 and was used to generate the PNO spectrum below 3000 K in the wavenumber range from 0 to 6000 cm-1. The millimetre wave spectrum agrees well with available experimental benchmarks. The Fermi resonance effects in the PNO spectrum are universal and complex, resulting in significant intensity increment of the related weak transition. This line list may be helpful for the spectroscopic characterization and possible astronomical detection of PNO, especially in high-temperature environments.

Reinvestigation of the ν3-ν6 Coriolis interaction in trifluoroiodomethane.

The lowest-frequency fundamental ν6 of trifluoroiodomethane (CF3I) has never been directly observed and analyzed at high resolution in the gas phase. The ν6(e) level interacts with ν3(a1) at 286.297 cm-1via a b-axis Coriolis interaction, which perturbs the rotational structure of both levels. In this work, we report low-J microwave transitions (for J ranging from 0-2) within the ν6 vibrational level. The l-type doubling observed in our spectrum agreed poorly with the predictions of previously published models of the interacting ν3-ν6 levels, prompting us to refine the model. We performed ab initio anharmonic force-field calculations, which were used to constrain some of the parameters, and which served as a check on some of the floated parameters. We fit a dataset consisting of 3593 transitions, which combined our measurements with previous microwave, millimeter wave, and high-resolution infrared observations. A reasonable set of fit parameters is obtained with ν6 = 267.28 cm-1, but we cannot rule out a lower value of ν6 = 261.5 cm-1 consistent with analyses of the vibrational level structure.

Ro-vibrational Spectrum of Linear Dialuminum Monoxide (Al2O) at 10 μm.

Dialuminum monoxide, Al2O, has been investigated in the laboratory at mid-IR wavelengths around 10 μm at high spectral resolution. The molecule was produced by laser ablation of an aluminum target with the addition of gaseous nitrous oxide, N2O. Subsequent adiabatic cooling of the gas in a supersonic beam expansion led to rotationally cold spectra. In total, 848 ro-vibrational transitions have been assigned to the fundamental asymmetric stretching mode ν3 and to five of its hot bands, originating from excited levels of the ν1 symmetric stretching mode and the ν2 bending mode. The measurements encompass 11 vibrational energy states (v1 v2l v3). The ro-vibrational transitions show spin statistical line intensity alternation of 7:5, which is caused by two identical aluminum nuclei of spin I = 5/2 at both ends of the centrosymmetric molecule of structure Al-O-Al. The less effective cooling of vibrational states in the supersonic beam expansion allowed measurement of transitions in excited vibrational states at energies of 1000 cm-1 and higher, while rotational levels within vibrational modes exhibited thermal population, with rotational temperatures around Trot = 115 K. Molecular parameters for 11 vibrational states were derived, including rotation and centrifugal distortion constants and l-type doubling constants for the states (v1 v2l v3) = (0 11 0) and (0 11 1) and an l-type resonance between the states (0 20 0) - (0 22 0) and (0 20 1) - (0 22 1). From the experimental results, rotational correction terms and the equilibrium bond length re were derived. The measurements were supported and guided by high-level quantum-chemical calculations that agree well with the derived experimental results.

Measurement of self-broadening coefficients and line intensities of ν1 + ν3 + ν4 ‒ ν4 band of acetylene in 1.5 μm spectral region: External cavity diode laser based absorption study

Acetylene is considered to be an important molecule for spectroscopic research due to its role in environmental chemistry, astrophysics, biochemistry and photochemistry of various planets. The high resolution spectroscopic studies of acetylene (12C2H2) in the 6474–6515 cm−1 spectral range have been performed using in-house developed external-cavity diode laser absorption spectroscopy technique. The study is focused on experimental measurement of self-broadening coefficients (γself) and line intensities of 27 l-doublet ro-vibrational lines belonging to the P-branch transition of ν1 + ν3 + ν4 ‒ ν4 hot band lying in the 6474–6515 cm−1 spectral range. The γself and line intensity have been retrieved by modelling of each experimentally observed rotational line with standard Voigt line profile using custom written python based computer program. The measured γself and line intensities were compared with the values present in HITRAN2020 database, showing mean difference of about -1.9% and 2.48%, respectively. In contrast to the line intensity, where rotational and symmetry dependency are readily visible, γself exhibits only rotational dependency. The l-type doubling constants of both ν1 + ν3 + ν4 and ν4 states of ν1 + ν3 + ν4 ‒ ν4 hot band have also been obtained. Detailed understanding of these molecular parameters will play an important role in modelling of planetary atmospheres.

Rotational dynamics and transitions between Λ-type doubling of NO induced by an intense two-color laser field.

We numerically investigate the rotational dynamics of NO in the electronic ground X2Π state induced by an intense two-color laser field (10 TW/cm2) as a function of pulse duration (0.3-25ps). In the short pulse duration of less than 12ps, rotational Raman excitation is effectively induced and results in molecular orientation. On the contrary, when the pulse duration is longer than 15ps, the rotational excitation is suppressed. In addition to the rotational excitation, we find that transitions between Λ-type doubling are induced. Significantly, the maximum coherent wave packet between Λ-type doubling in J = 0.5 is generated using the pulse duration of 19.8ps. The wave packet changes to the eigenstates of Λ = +1 or -1 alternatively, where Λ is the projection of the electronic orbital angular momentum on the N-O axis, which is regarded as the unidirectional rotation of an unpaired 2π electron around the N-O axis in a space-fixed frame as well as in a molecule-fixed frame. The experimental method to observe the alternation of the rotational direction of the electron around the N-O axis is proposed.

L-doublet splittings in Δ vibrational state of 15N14N16O isotopomer

We report the direct experimental evidences of l-doublet fine splittings between the parity doublet e and f sub-states of β-site isotopomer of nitrous oxide (15N14N16O) in the (1220)←(0220) ro-vibrational transition for l = 2 (i.e. Δ state) vibrational state in the mid-IR 7.8 µm spectral region. Due to extremely small splittings it remains a challenge for recording the fine structure doubling features for l = 2 or higher states. The existence of l-type doubling was investigated by high-resolution and ultra-sensitive cavity ring-down spectroscopy coupled with an external-cavity quantum cascade laser. We determined several new spectroscopic parameters such as l-type doubling constants, Coriolis constants, band centres, rotational constants and centrifugal distortion constants for l = 2 state of β-site N2O isotopomer by probing the rotationally resolved spectral lines with higher J values in the P-branch. Subsequently, the pressure broadening effect on the l-doublets and the corresponding broadening coefficients for both e and f sub-states in Δ state of β-site N2O were explored. Our high-resolution spectroscopic measurements will be useful for better fundamental understanding of linear polyatomic molecules and their isotopomers.

Cavity ring-down spectroscopy of l-type doubling in 15N-β-site N2O isotopomer near 7.8 µm

The spectroscopic features of l-type doublets of the site-specific 15N-isotopomers of nitrous oxide (N2O) are interesting to study as it would reveal the effect of l-type doubling in different branches of the transition band and on the spectroscopic parameters. Here, we have explored various spectroscopic features that are influenced by the l-type doubling of the fine structure lines of the β-site isotopomer of N2O, i.e. 15N14N16O (or 15Nβ) in the (1110)←(0110) transition for l = 1 (i.e. Π state) vibrational state in the mid-IR region. High-resolution spectroscopic measurements of rotationally-resolved l-type splitting involving the parity doublet e and f sub-states of 15N-β isotopomer corresponding to the P-and R-branches of the (1110)←(0110) vibrational band near 7.8 μm were carried out by cavity ring-down spectroscopy (CRDS) coupled with a continuous-wave external-cavity quantum cascade laser (cw-EC-QCL). Several new spectroscopic parameters such as l-type doubling constants, Coriolis constants, band centres, rotational constants and centrifugal distortion constants were determined for both the parity doublet e and f components of 15Nβ isotopomer. We also investigated the effects of temperature and pressure on the l-type doublets along with the dependency of pressure broadening coefficients on the rotational quantum number J. The new experimental data will improve our understanding of the molecular properties of the site-specific 15N-isotopomers of N2O and intramolecular distribution of 15N-isotopes within the N2O isotopomers.

Profiling astrophysically relevant MgC4H chains. An attempt to aid astronomical observations

ABSTRACT In this paper, we report results of an extensive theoretical study on MgC4H chains conducted at DFT and CCSD(T) levels motivated by the recent discovery of this species in IRC+10216. A detailed characterization of both neutral and charged species is presented, which include structural, chemical bonding and vibrational properties, rotational, centrifugal distortion and Watson l-type doubling constants, dipole moments, Fermi contact, and spin-rotation constants. In addition, we present ab initio estimates needed for subsequent astrochemical evolution modelling (e.g. dissociation energies, acidity, electron attachment, and ionization energies and related chemical reactivity indices). Possible formation pathways are also discussed. They comprise exchange, (radiative) association, dissociative recombination, and ion neutralization reactions. As an important result aiming at stimulating further observational searching, we suggest that MgC4H− anions should also be observable via rovibrational spectroscopy. The reason is twofold: (i) Neutral MgC4H0 chains possess a sufficiently large dipole moment consistent with dipole-bound anion states and large electron attachment cross-sections. (ii) MgC4H− anions possess a dipole substantially larger than MgC4H0 neutrals (and also larger than that estimated earlier for the longest astronomically detected C8H− anion). This makes MgC4H− anion intensities in rovibrational spectrum experimentally accessible even in the unlikely case of a relative abundance MgC4H−/MgC4H0 comparable to that of CH4, whose anion has the lowest relative abundance observed so far in space because weakly polar C4H0 chains do not support dipole-bound anion states. A suggestion on why, counterintuitively, the MgC2H abundance found in IRC+10216 was lower than that of the longer MgC4H is also presented.

Cavity ring-down spectroscopy measurements of l-type doubling of hot bands in Δ vibrational states of OCS near 5.2 μm

We investigated the l-type doubling in the (1420) ← (0220) weak hot band transition of carbonyl sulphide (OCS) for l = 2 (i.e. Δ state) vibrational state. High-resolution spectroscopic measurements of l-doublet splittings of OCS were carried out using cavity ring-down spectroscopy (CRDS) technique employing a continuous-wave (cw) external-cavity quantum cascade laser (EC-QCL) operating at ∼5.2 μm. The rotationally resolved spectra of l-doublet splittings between the parity doublet e and f sub-states of OCS were recorded by probing the rotational lines from J = 22 to J = 29 in the R branch belonging to the weak hot band transition. Subsequently, we determined the l-type doubling constant, transition dipole moment, rotational constant and centrifugal distortion constant for both e and f components of the (1420) vibrational state with relatively high rotational states of OCS. As the measurement of l-doublet splitting in l = 2 or higher states of OCS remains challenging due to extremely small splitting, therefore our findings suggest that the observation of the l-type doubling in Δ vibrational state (l = 2) with new values of the several spectroscopic parameters as mentioned above will be useful for better understanding of linear polyatomic molecular properties in general from high-resolution spectroscopic data.

Determination of ν2 fundamental band origin for BeH2 and BeD2 from deperturbation analysis of hot bands.

New vibration-rotation hot bands, i.e., 031 → 030 and 041 → 040, have been assigned and rotationally analyzed for the gaseous BeH2 molecule. The 03(1)0 (Πu), 03(1)1 (Πg), 04(2)0 (Δg), and 04(2)1 (Δu) states are locally perturbed by the nearby 001 (Σu (+)), 002 (Σg (+)), 01(1)1 (Πg), and 01(1)2 (Πu) states, respectively [A. Shayesteh et al., J. Chem. Phys. 118, 3622 (2003)]. Appropriate Hamiltonian matrices have been constructed to take the effects of rotational ℓ-type doubling, ℓ-type resonance, and third order Coriolis interactions into account, and used in deperturbation analyses. From nonlinear least squares fits of all the data, relative energies and unperturbed rotational constants have been determined for the 030, 031, 040, and 041 vibrational levels of BeH2. Similar deperturbation fits were performed for the 001 → 000 and 011 → 010 bands of the BeD2 isotopologue, while the 030 and 040 vibrational levels were treated as dark states. From relative vibrational energies of the 030 and 040 levels, the ν2 fundamental band origins were determined to be 711.48 ± 0.05 cm(-1) and 548.21 ± 0.1 cm(-1) for BeH2 and BeD2, respectively.

Deperturbation of the 011 → 010 hot band for ZnH2 and ZnD2

Local perturbations observed in the 0111 (Πg)→0110 (Πu) hot bands of 64ZnH2, 66ZnH2, 68ZnH2, 64ZnD2 and 66ZnD2 have been analyzed. The 0111 (Πg) state is perturbed by the nearby 040 vibrational level that contains 0440 (Γg), 0420 (Δg) and 0400 (Σg+) states. Appropriate Hamiltonian matrices were constructed in which the effects of rotational ℓ-type doubling, ℓ-type resonance and Coriolis interaction were taken into account, and nonlinear least squares fits were performed. Unperturbed constants were obtained for the 0111 (Πg) states, along with vibrational energies of the 040 (perturbing) levels and the Coriolis interaction coefficients. Relative vibrational energies of the 040 and 030 levels were then used to estimate the origins of the bending mode fundamental bands, resulting in ν2 vibrational wavenumbers of 634.45cm−1 and 459.14cm−1, for 64ZnH2 and 64ZnD2, respectively.

Millimeter-wave spectroscopy of the FeCO radical in the ν2 and ν3 vibrationally excited states.

The pure rotational spectra of the FeCO radical in the ν2 (bending) and ν3 (Fe-C stretching) vibrational states of the ground X̃(3)Σ(-) electronic state were observed in the millimeter-wave region. The equilibrium rotational and centrifugal distortion constants were determined to be Be = 4374.631 (58) MHz and De = 1.1666 (20) kHz together with the spin-spin coupling constant λe = 691.89 (37) GHz and spin-rotation coupling constant γe = - 1079.4 (55) MHz with use of the millimeter-wave results and the ν1 IR data. The equilibrium bond length for Fe-C was derived to be 1.725 Å assuming that for C-O to be 1.159 Å. Since the vibronic symmetry of the excited state of bending vibration is (3)Π, the analysis of spectrum in the ν2 state required an effective spin-orbit interaction constant of A2 = 6.0219 (61) GHz together with three parity doubling constants of o2 = 36.168 (10) GHz, p2 = 85.18 (34) MHz, and q2 = 4.7024 (17) MHz. The effective spin-orbit interaction constant A2 is attributed to the vibronic mixing of the (3)Π excited electronic states. The vibronic mixing also cause the parity doubling constants o2 and p2, but the main contribution to q2 is given by the vibrational l-type doubling.

The high-resolution infrared spectrum of DC4H from 450 to 1100 cm−1: Overtone, combination, and hot bands

The high-resolution infrared spectrum of monodeuterated diacetylene has been recorded in the 450-1100 cm(-1) spectral region by Fourier transform infrared spectroscopy. Seven new bands have been identified: the ν3 fundamental (C-C stretch), and the ν8 + ν9, ν7 + ν8, 2ν7, 2ν8, ν8 + ν9 - ν9, and ν6 + ν9 - ν9 combination, overtone, and hot bands. The assigned transitions, together with those previously reported for the fundamental bands [F. Tamassia, L. Bizzocchi, C. Degli Esposti, L. Dore, M. Di Lauro, L. Fusina, M. Villa, and E. Canè, Astron. Astrophys. 549, A38 (2013)], form a comprehensive data set which comprises more than 2500 ro-vibrational transitions, and involves all singly and most doubly excited vibrational states of DC4H lying below 1000 cm(-1). Rotational and vibrational l-type resonance effects among the sub-levels of excited bending states were considered in the analysis, which also included a careful treatment of the various anharmonic interactions coupling many vibrational states lying above 600 cm(-1). Reliable and unambiguous spectroscopic parameters were obtained for each investigated state, including the rotational and centrifugal distortion constants Bv and Dv, the l-type doubling parameter qt, the anharmonicity constants xL(89), xL(69), and the vibrational l-type terms r89, r69 for the v8 = v9 = 1 and v6 = v9 = 1 bend-bend combination states.

Spectroscopic Study of N2(b1Πu, ν = 8) by Atmospheric-Pressure Resonant-Enhanced Multiphoton Ionization and Fluorescence Detection

A spectroscopic analysis of the strongly perturbed N2(b(1)Πu, ν = 8) state has been conducted, accounting for b(1)Πu(ν = 8) ← X (1)Σg(+)(ν = 0) transitions, for the first time, up to J' = 20. A novel laser spectroscopy technique, using a combination of resonant-enhanced multiphoton ionization and fluorescence detection at atmospheric pressure, avoids the severe effects of perturbation reported in past extreme vacuum ultraviolet absorption experiments that produced weak and unusable spectra for the ν = 8 level. The R, Q, and P branches of the three-photon absorption transition b(1)Πu(ν = 8) ← X(1)Σg(+)(ν = 0) were fit, allowing rotational term energy assignment up to J' = 20 and molecular constants to be determined. Evidence of the previously suspected perturbation in b(1)Πu(ν = 8) is clear in this data, with significant Λ-type doubling at higher J' along with an anomalous negative value determined for the centrifugal distortion coefficient.

The ν5 antisymmetric stretching mode of linear C7 revisited in high resolution

The nu(5) antisymmetric stretching mode of the linear carbon cluster C(7) has been revisited using a sensitive high-resolution spectrometer, including an external-cavity quantum cascade laser covering the range of interest of 1894-1901 cm(-1). 50 transitions of the nu(5)-band have been recorded and analyzed together with 45 transitions of the nu(4)-band measured by Neubauer-Guenther et al. [J. Chem. Phys. 127, 014313 (2007)]. We determined the band centers, rotational and centrifugal constants very precisely. In addition, 29 hot band transitions have been measured and tentatively assigned to the nu(5)+nu(11)-nu(11) hot band. A global fit of the hot bands nu(5)+nu(11)-nu(11) and nu(4)+nu(11)-nu(11) is presented. Derived l-type doubling constants allow for an experimental estimation of the nu(11)-band center.

Rotational Spectrum of NSF3 in the Ground and v5 = 1 Vibrational States: Observation of Q-Branch Perturbation-Allowed Transitions with Δ(k − l) = 0, ±3, ±6 and Anomalies in the Rovibrational Structure of the v5 = 1 State

The rotational spectrum of NSF3 in the ground and v5 = 1 vibrational states has been investigated in the centimeter- and millimeter-wave ranges. R-branch (J + 1 <-- J) transitions for J = 0, 1 and Q-branch rotational transitions for the v5 = 1 vibrational state have been measured by waveguide Fourier transform microwave spectroscopy in the range 8-26.5 GHz. The Q-branch transitions include 28 direct l-type doubling transitions (kl = +1, A1) <--> (kl = +1, A2) with J < or = 62, and 108 direct l-type resonance transitions following the selection rule delta k = delta l = +/-2 with J < or = 60 and G = |k - l| < or = 3. A process called "regional resonance" was observed in which a cluster of levels interacted strongly over a large range in J. This process led to the observation of 55 perturbation-allowed transitions following the selection rules delta(k - l) = +/-3, +/-6. In particular, (kl = +1, A+) <--> (kl = -2, A-), (kl = +4, A+) <--> (kl = +1, A-), (kl = +2) <--> (kl = -1), (kl = +3) <--> (kl = 0), (kl = +2) <--> (kl = -3), and (kl = +3) <--> (kl = -3). The various aspects of the regional resonances are discussed in detail. An accidental near-degeneracy of the kl = 0 and kl = -4 levels at J = 26/27 led to the observation of perturbation-allowed transitions following the selection rule delta(k-l) = +/-6 with (kl = +2) <--> (kl = -4). A corresponding near-degeneracy between kl = -1 and kl = -3 levels at J = 30/31 led to the detection of similar transitions, but with (kl = +3) <--> (kl = -3). In the range 230-480 GHz, R-branch rotational transitions have been measured by absorption spectroscopy up to J = 49 in the ground-state and up to J = 50 in the v5 = 1 vibrational state. The transition frequencies have been analyzed using various reduced forms of the effective Hamiltonians. The data for the v5 = 1 vibrational state have been fitted successfully using two models up to seventh order with delta k = +/-3 interaction parameters constrained (dt constrained to zero, and epsilon to zero or to the ground-state value). On the other hand, reductions with the (delta k = +/-1, deltal = -/+2) interaction parameter q12 fixed to zero failed to reproduce the experimental data since the parameters defining the reduction transformation do not arise in the correct order of magnitude. The ground-state data have been analyzed including parameters up to fourth order constraining either parameters of the delta k = +/-3 interactions to zero (reduction A), or of the delta k = +/-6 interactions to zero (reduction B). The unitary equivalence of the different parameter sets obtained is demonstrated for both vibrational states.

Coupled cluster calculations for (potential) interstellar anions: The C2nH− series (n = 2–6)

The coupled cluster variant CCSD(T) in conjunction with a large basis set has been used to calculate spectroscopic properties for anions of type C2nH− (n=2–6), three of which were recently observed in the interstellar medium by means of radio astronomy. Accurate equilibrium structures and electric dipole moments are predicted for all five species. A variety of spectroscopic constants (vibrational wavenumbers, vibration–rotation coupling constants, l-type doubling constants and centrifugal distortion constants) are reported for various isotopomers of C4H− and C6H−. The harmonic bending vibrations of chains up to C10H− and HC9N are analyzed by means of “mass plots” which draw the wavenumbers of interest as a function of the “hydrogen” mass, which is regarded as a continuous variable.

A note on l-type doubling constants in linear triatomic molecules ClHCl −: A molecular anion with an unusual q

In this note it will be recalled that the sign of the quantity which is called l-type doubling constant in linear triatomic molecules is determined by two factors which are independent. The first factor depends on the construction of the wavefunction describing the rovibrational motion of the linear molecule. The second one is a result of the interplay between the molecular potential energy function and the atomic masses. The latter effect makes in almost all linear triatomic molecules the same contribution to the sign. In this paper an exception to this rule will be presented: ClHCl − shows an unusual l-type coupling constant.

The pure rotational spectrum of CrCN (X 6 Σ +): an unexpected geometry and unusual spin interactions

The pure rotational spectrum of CrCN (X 6Σ+) has been recorded in the frequency range 250–520 GHz using direct-absorption techniques. This is the first spectroscopic investigation of the CrCN radical. This species was synthesized by reacting Cr vapour with (CN)2. Spectra were obtained for the main isotopic species, the 53Cr and 13C isotopologues, and the heavy atom stretch and several quanta of the bending vibration. The molecule was found to have a linear cyanide geometry and a 6Σ+ ground state. Rotational, fine structure, and l-type doubling constants have been determined. The spin–spin parametre λ was found to be small–a likely result of competing second-order spin–orbit contributions from excited 4Σ−, 4Π, and 6Π states. However, λ increased significantly in the bending mode, which may be caused by a reduction of the 6Σ+−4Π interaction strength due to spin–orbit vibronic coupling. In contrast, the value of γ, arising from interactions with a nearby 6Πstate, was independent of v 2. The CrCN bond lengths were determined to be r Cr–C = 2.019 Å and r C–N = 1.148 Å. Delocalization of the 3dπ electrons into the CN 2π* orbital, which is polarized towards the carbon atom, may account for the CrCN structure.