Calculation of the potential energy curves for the low-lying doublet and quartet states of the CN radical

The potential energy curves of the low-lying X²Σ⁺, A²π_i, B²Σ⁺,⁴Σ⁺, and ⁴π states of CN are calculated by the MC SCF (CAS SCF) method. Their vibrational levels and the molecular constants obtained are in good agreement with those determined in our recent experimental analysis of the CN (B²Σ⁺-X²Σ⁺) emission spectrum. several intensity anomalies in the observed spectrum are ascribed to perturbations between the B²Σ⁺ and ⁴π states with the following vibrational quantum numbers: (υ_B, υ_π)=(9,x), (11, x+2), (12, x+3), (14, x+6), (17, x+11), and (18, x+13), where x = 0 is the most probable assignment. Likewise, the perturbations between the B²Σ⁺ and ⁴Σ⁺ states with (υ_B, υ_Σ) = (11, y), (13, y+3) are interpreted as y = 8±1.     

Sensitization of the CN(B2Σ+ → X2Σ+) emission by Hg(63P0) metastables

The vibrational analysis of the CN(B²Σ⁺ → X²Σ⁺) emission sensitized by Hg(6³P₀) metastables has shown that the energy transfer process, Hg(6³P₀) + CN(X²Σ⁺) → Hg(6¹S₀) + CN(B²Σ⁺), populates the CN(B²Σ⁺) state in a non-Franck-Condon fashion. The relative vibrational populations for the ν = 0 to 4 states are 1.00, 0.56 ± 0.06, 0.26 ± 0.03, 0.11 ± 0.03 and 0.04 ± 0.01, respectively. Long-range attractive interaction between the Hg(6³P₀) atom and the CN(X²Σ⁺) radical is evidenced by the observed high rotational excitation of the CN(B²Σ⁺) radical following the energy transfer process.     

Formation of CN(B2Σ) by the electron impact dissociation of HCN. measurements near threshold

Emission spectra of the CN violet band system (B²Σ—X²Σ) were observed by the electron impact on HCN with several impact energies near the threshold. The formation of CN(B) by the dissociative excitation of HCN was investigated. The threshold energy agreed essentially with that obtained by the photodissociation measurements by Okabe et al. The excitation function and the dependence of the vibrational populations of CN(B) on the electron energy were obtained. These results suggest that an optically allowed state contributes to the formation of CN(B) from HCN as a main precursor.     

Photoluminescence spectroscopy of the CN radical produced in the infrared photolysis of CH3CN

The infrared laser-induced photolysis of CH₃CN has been studied by observing luminescence from the excited CN (B²Σ⁺) radical and pulsed dye laser-induced fluorescence of ground state CN(X²Σ⁺), both produced as primary fragments. Both temporal and wavelength resolved spectroscopy have been performed on the luminescence, whereas pulsed dye laser probing has allowed time-resolution of the CN(X²Σ⁺) radical as well as measurements of the decay time of the CN(B²Σ⁺) state produced in the dye laser pumping. A reaction mechanism, characterizing the observed results, is proposed.     

Franck-Condon Factors for the Transitions N2, C 3πu → B 3πg and CN,B 2 Σ + → X 2 Σ +

Franck-Condon factors for the transitions N₂, C ³π_u→ B ³π_g and CN, B ² Σ ⁺ → X ² Σ ⁺ have been calculated by the method of Chang and Karplus.     

Oscillator strength of the CN A 2Πi → B 2Σ+ (0,0) transition

The relative oscillator strength of the A ²H_i → B ²Σ⁺ transition has been measured by comparing the laser-induced fluorescence signal from excitation of a known distribution of CN A ²H_i and CN B ²Σ⁺ produced by the photodissociation of cyanogen at 158 nm. The oscillator strength of the A ²H_i → B ²Σ⁺ transition is 0.011 ± 0.006 times that of the X ²Σ⁺ → B ²Σ⁺ system. This leads to a value of (4.0 ± 2.2) × 10^?4 for the band oscillator strength.     

Dynamics of formation of CN(B2Σ+) fragment from HCN and DCN in an argon afterglow

The dissociative excitation of HCN and DCN producing CN(B²Σ⁺) in collision with Ar(³P_0,2) was investigated in a flowing afterglow. The Δν = 0, ?1, and ?2 sequences of the CN(BX) violet emission were analyzed by computer simulation, and the vibrational and rotational distributions of the CN(B²Σ⁺) fragment were obtained. Possible reaction pathways were studied on the basis of a linear surprisal analysis of the observed distributions and their isotope effects.     

Rotational excitation and the energy distribution of CN(B2Σ) produced by the reaction of metastable Ar(3P0,2) atoms with HCN

The violet emission spectrum (B²ΣX²Σ) of the CN radical observed by the collision of HCN with metastable Ar(³P_0,2) atoms was analyzed. The effective rotational temperature of the CN(B²Σ) radical, as estimated from a band envelope analysis, is about 2000°K. The distributions of the excess energy to vibration, rotation and translation are found to be 1.2 ± 0.2, 0.2 and 1.9 ± 0.3 eV, respectively.     

Isotope effects in photofragmentation of linear triatomics

We report the results of a theoretical study of isotope effects on the predissocation lifetimes, on the absorption cross sections for direct photodissociation and on the vibrational distribution of the photofragments in the photofragmentation of HCN and DCN. The deuterium isotope effect on the photofragmentation probability at 1.45 eV above the thréshold for production of CN (B²Σ) is γ_s(DCN)/γ_s(HCN) ≈ 0.2.     

Kinetics of CN(v=0) and CN(v=1) with H2 HCl and HBr

CN radicals have been generated in their X ²Σ⁺ (v=0) and (v= 1 ) levels by pulsed laser photolysis of NCNO at 532 nm, and time-resolved laser-induced fluorescence has been used to measure the rates of their removal by H₂, HC1 and HBr. The rate constants for removal of CN(v= 1 ) by these three species are 1.2 ± 0.3, 1.1 ± 0.2 and 1.3 ± 0.1 times the rate constants for reaction of CN(v=0). The results can be interpreted in terms of vibrationally adiabatic theory and a CN vibrational frequency which is almost the same in the transition state as in the isolated radical.     

Test ofBΣ-interaction potentials in Na 3P-rare gas systems from light scattering

The spectral dependences in Na-rare gas optical collisions $$Na3S + X + hv \to Na3P_J + X$$ have been used to study the long range interaction in Na 3P _J -X systems. For a test of available potentials the fine structure (fs) population ratio and theJ = 3/2 alignment were measured under single collision conditions by analyzing the fluorescence emitted after selective excitation of the molecularBΣ orAΠ states as function of the laser frequencyv. A comparison was made with quantum coupled channels (CC) calculations of thermally averaged spectral profiles using the potential data to be tested as input. In addition, model calculations were performed for a qualitative understanding of the role of the various nonadiabatic couplings involved and the trends in the spectral profiles by the corresponding molecular potentials. In NaAr and NaKr theBΣ-fs wings are seen to depend sensitively on the parameters of the potentials, in particular on the well depth? _ΣII of theBΣ-AΠ difference potentials which is comparable to the spin orbit interaction in these systems; the experimental profiles show, that the actual? _ΣII values are much smaller than those predicted by the model potentials of Düren. In NaKr also theBΣ-alignment wing depends sensitively on? _ΣII caused by a long-range parity dependent rotational coupling, as follows from the CC-analysis. The comparison with the experimental alignment confirms the result from theBΣ-fs wing regarding the actual? _ΣII value.     

Test of the asymptotic method as applied to atom-diatom interaction potentials

The accuracy of the asymptotic method in calculating long-range atom-diatom exchange interactions is tested for two sample systems. In both cases high-quality ab initio results are available for comparison. As a first example, the energy splitting between theA′ andA″ surfaces arising from OH(X ²Π)+Ar were expressed analytically in terms of asymptotic parameters of the O and Ar atoms. The agreement with the calculated ab initio quantity is very good for a range of interatomic distances and different angles of approach. Secondly, for the system CN+He, the diabatic off-diagonal matrix elementV _ΣA′ between two diabaticA′ potential energy surfaces arising from CN(X ²Σ⁺)+He and CN(A ²Π)+He is considered. Using the asymptotic approach, this element can be expressed in terms of the three diagonal matrix elements for CN(X andA)+He which are known ab initio. The resulting values ofV _ΣA′ are found to be in very good agreement with the directly ab initio calculated coupling matrix element over a wide range of CN-He geometries.     

150−230 nm Chemiluminescence from C,CN and CO and observation of C(3P, 1D) in the N/C2F4 and N/O2/C2F4 reactions

Addition of C₂F₄ to a flowing nitrogen afterglow gives rise to CN(E²ΣA²Π, X²Σ), CN(F² ΔA²Π) and C (156.1, 165.5 and 193.0 nm) chemiluminescence. Transitions have been observed from CN(E²Σ) up to ν′ = 2 from which vibrational constants for this state have been recalculated to be ω_eχ_e = 13.8 cm^?1 and ω_e = 1698.4 cm^?1. Ground state and metasrable C(³P, ¹D) have been detected and studied via resonance fluorescence. Addition of O₂ to the N/C₂F₄ reaction system reduces C and CN emission intensities and [C] while giving rise to CO(a³Π-X¹Σ), CO(A¹ΠX¹Σ) and NO(B²ΠX²Π) emission. Probable excitation mechanisms are discussed.     

Photoexcitation of CH3NCO,CH3NCS and CH3SCN in the vacuum ultraviolet: Rydberg states and photofragment emission

Photoabsorption cross sections and fluorescence excitation spectra of CH₃NCO, CH₃NCS and CH₃SCN vapor were measured in the vacuum ultraviolet using synchrotron radiation. Many sharp structures observed from CH₃NCO and CH₃SCN in the 120–180 nm region are classified into three Rydberg series and their vibrational progressions, whereas for CH₃NCS six broad bands exhibit no fine structure. The emission which starts to appear at 172.8 ± 1.0 nm excitation of CH₃NCO is attributed to the NCO(A²Σ⁺-X²Π) band. The emissions from CH₃NCS and CH₃SCN are assigned to the A²Π-X²Π and B²Σ⁺-X²Π bands of NCS; the CN(B²Σ⁺-X²Σ⁺) band is also observed at 125 nm excitation of CH₃SCN. The photodissociation processes are discussed in accord with the emission observed.     

Der Cyano-nitro-bis-biacetyldioximato-kobalt(III)-Komplex und seine Aquatisierungskinetik in saurem Medium

The [Co(BH)₂(CN)(NO₂)]^? complex (BH₂ = biacetyldioxime) has been obtained by means of an anatation reaction from the [Co(BH)₂(NO₂)(H₂O)] nonelectrolyte with KCN in aqueous solution. The free acid H[Co(BH)₂(CN)(NO₂)]·4 H₂O and 12 derivatives were obtained by double decomposition reactions. The thermal decomposition of some of these compounds was thermogravimetrically studied. Kinetics of the aquotization of the [Co(BH)₂(CN)(NO₂)]^? was investigated in acid solution by following the change of the concentration of the free NO₂ ^?-ions by means of a diazotation reaction. The kinetic parameters of the reaction are given.     

Raman study of molecular dynamics of inorganic fluoroxidizers in nonaqueous solutions—Part 1. Xenon difluoride in acetonitrile

The Raman spectra of the totally symmetric ν₁(Σ_g⁺) mode of XeF₂ molecules have been measured in CH₃CN solutions at various temperatures and concentrations. The vibrational and rotational correlation functions as well as the characteristics times have been calculated. It was concluded that the vibrational band width in these solutions is to be attributed to the vibrational dephasing, whereas the contribution from the rotational relaxation has been found to be of less importance.     

C2 and CN formation by optical pumping of CO/Ar and Co/N2/Ar mixtures at room temperature

A continuous wave carbon monoxide laser is used to excite the vibrational mode of CO in CO/Ar and CO/N₂/Ar mixtures flowing through a gas absorption cell. High steady-state excitation of the CO vibrational mode (0.3 eV/molecule) is achieved, while a translational—rotational temperature near 300 K is maintained by the steady flow of cold gas into the cell. These non-equilibrium conditions result in extreme vibration—vibration pumping, population high-lying vibrational quantum levels (to V = 42) of CO. N₂ can also be pumped by vibrational energy transfer from CO. Under these conditions, C₂ and CN molecules are formed, and are observed to fluoresce on various electronic band transitions, notably C₂ Swan (A ³Π_g—X ³Π_u) and CN violet (B ²Σ⁺—X²Σ⁺).     

Fluorescence and recombination-emission spectra from S2 formed by ultraviolet laser photolysis of CS2 in an argon matrix at 15 k

Two series of emission bands were observed for the CS₂/Ar(1 : 100–500) system at 15 K with excitation at 257.3 nm. They are assigned to B³Σ^?_u → χ³Σ^?_g and B″³Π_u → X³Σ^?_g of S₂, which was formed by photodissociation of CS₂, CS₂ + hv → CS + S, followed by recombination of two S atoms. The B″³Π_u state has been found 524 cm^-1 lower in energy than B³Σ^?_u     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

The infrared spectrum of chd2cn and the ground state geometry of methyl cyanide

Analysis of the rovibration spectrum of CHD₂CN enables the rotation parameter (A_o—B?_o) to be determined, from which the value of A_o may be found using the microwave B_o and C_o constants. The use of A_o (CHD₂CN) in conjunction with all other available B_o and C_o constants for isotopes of methyl cyanide enables the ground state geometry to be defined within fairly narrow limits. The CH bond length is in agreement with the value predicted from the CH vibration frequency of CHD₂CN, and with the value calculated from the results of a recent analysis of the infrared spectrum of CD₃CN.