Penning Ionization of NCCN by Experiment and Theory:  A Two-Dimensional Penning Ionization Electron Spectroscopic and Quantum Chemical Study

Abstract

Dicyanogen, NCCN, is generated for spectroscopic investigations on-line from rubeanic acid, mercury(II) cyanide, and cyanogen iodide and studied in the gas phase by two-dimensional Penning and He I photoelectron spectroscopies, as well as ab initio calculations. From spectroscopic data, the interaction between NCCN and He*(23S) atoms is deduced. The interaction potential for the similarly interacting NCCN−Li(22S) system is obtained from ab initio calculations at the CCSD/6-311++G** level. Experimental and calculated results show that the interaction potential is anisotropic around NCCN, is the most attractive in the nitrogen lone electron pair region, and gradually changes into repulsive as the N−C−He*(or Li) angle opens up to 90°. An unusual collision energy dependences of the partial ionization cross sections are observed, which is interpreted by the unusual interaction potential. For assisting experimental data and studying collision dynamics, classical trajectory calculations are performed for the Penning ionization of the NCCN−He*(23S) system. The spectroscopic investigations predict the existence of thermodynamically stable MLi radicals, and the structure and stability of NCCNLi isomers are calculated at the QCISD/6-311++G** level.

Penning Ionization of (NH2)2CX (X = O, S) with He*(23S) Metastable Atoms. Difference of Anisotropic Interaction around N, O, and S Atoms

“…The weak attractive interactions around the “nitrogen lone pair” of urea and thiourea are unexpected and interesting, because the interaction around the lone pair of the amino group in C 3 H 5 NH 2 has been known to be strongly attractive, with a potential well depth of ca. 400 meV, and an attractive interaction around the “lone pair” was a general trend in previous studies. ,− ,− It should be noted that similar unexpected weak interactions around “nitrogen lone pair” was found for amide compounds…”

“…In addition, it should be noted that geometry optimization was performed with ab initio calculation for H 2 CX...LiF (X = O, S), and n σ lone pair donation was found for the oxygen compound and n π lone pair donation was found for the sulfur compound. On the other hand, a strong attractive interaction was found for the lone pair n N orbital region of cyclopropylamine (C 3 H 5 NH 2 ) and nitriles. ,, In addition, to obtain CEDPICS of NCCN by collision with He*(2 3 S), a classical trajectory calculation was performed on the highly symmetric ( D ∞ h ) potential energy surface with attractive interaction around the N atoms …”

Spin−Orbit Coupling Effect and Intramolecular Orbital Interactions: Penning Ionization of CH2BrCl, CHBrCl2, and CH2BrCN by Collision with He*(23S) Metastable Atoms

“…However, a distinguished enhancement of band 5 in Figure cannot be explained by the extensive electron distribution of the corresponding MO 19a‘( n N ), it is owed to strong attraction for the He* access along the CN axis. This phenomenon was observed in CERPIES of nitrile compounds. ,− Band 9 in Figure is enhanced significantly in the PIES with respect to that in the UPS because the corresponding 20a‘ orbital has some characteristics of C 2s orbital (see Figure ), and it has been noted that the resonant excitation transfer and the subsequent autoionization frequently occurs for the C 2s bands 1 Band Assignments, Ionization Potentials (IP, eV), Peak Shifts (Δ E , meV), and Slope Parameters ( m ) for CH 2 BrCl bandIP obsd IP OVGF (pole strength)orbital characterΔ E m 1 a 10.75 10.62 (0.94) 8a‘ ‘( n Br ⊥ ) −80 ± 10 −0.35 2 a 11.08 10.65 (0.94) 22a‘( n Br ∥ ) −50 ± 20 −0.36 3 11.79 11.43 (0.92) 21a‘ ‘( n Cl ∥ ) −60 ± 10 −0.31 4 11.50 (0.92) 7a‘ ‘( n Cl ⊥ ) 5 14.63 14.40 (0.92) 20a‘(σ CBr ) −20 ±20 −0.21 6 15.40 15.28 (0.91) 19a‘(σ CCl , σ CH ) −10 ± 40 −0.22 7 16.32 16.59 (0.90) 6a‘ ‘(π CH ) −10 ± 80 −0.19 S* 17.9−18.2 b −0.16 a Spin−orbit split bands (details discussed in text).…”

“…It is well-known that the shape of velocity dependence of the total scattering cross section of He*(2 3 S) by He, Ar, and Kr is very similar to that of Li(2 2 S),37a and interaction well depths and locations of potential wells have been found to be very similar for interactions of various targets with He*(2 3 S) and Li(2 2 S). ,37b,c So this similarity between He*(2 3 S) and Li(2 2 S) is usually used to compare the computationally much more feasible Li−M potentials with the experimental results on the He*(2 3 S)−M interactions. − ,29a In this study, the interaction potential calculations with the Li(2 2 S) atom, V* ( R ,θ,φ) (where R , θ, and φ were defined in the figures), were performed at the unrestricted MP2 level of theory using the 6-31+G(d,p) basis set with scanning R , θ, or φ values and the geometrical parameters of the targets fixed at the previously optimized values. Spin contamination is negligible for these calculations.…”

“…Recently, a series of CERPIES and CEDPICS studies have been reported for specific molecules having a cyano (CN) group (CH 3 SCN, CH 3 CN, C 3 H 5 CN, NCCN, CH 3 CH 2 CN, CH 2 CHCN, CH 2 CHCH 2 CN 12 ). These results indicate that the interaction potentials between He*(2 3 S) and π CN orbitals are strongly attractive around the cyano group.…”