Photoelectron spectroscopy of CH2N−

Abstract

We have measured the negative ion photoelectron spectra of CH2N− and CD2N− and find the electron affinities: EA(CH2N)=0.511±0.008 eV and EA(CD2N)=0.498±0.011 eV. Franck–Condon simulations of these spectra are carried out and we estimate the CH2N− and CH2N geometry differences; we fit our spectra with the following [constrained] molecular structures. We combine our EA(CH2N) with the results of previous gas phase ion studies to extract a number of thermochemical parameters (kcal/mol): Do0(CH2N–H)=85±5, Do0(H–HCN)=23±6, Do0(H2C–N)=144±6, and the isomerization enthalpy of H2CN+→HCNH+ is ΔHisom(C2v→C∞v)=−51±7. Attempts to calculate the geometry and vibrational frequencies of the H2CN radical are disappointing. Unrestricted Hartree–Fock and second-order Mo/ller–Plesset ab initio calculations in a 6-31++G** basis produce badly spin-contaminated wave functions which do not reproduce the experimental findings.

Electron collisions with the H2CN radical using theR-matrix method

“…To provide additional information on the charge distribution in the H 2 CN molecule, we have also calculated the dipole and quadrupole moments. The dipole moment of μ value at the ground state is predicted to be 2.476 D, which is in good agreement with the value 2.54 D reported by Cowles [18]. The difference in the two is due to the inclusion of correlation effects lowering the value of the dipole moment in the CI model.…”

“…The energy of the highest occupied MO 1 A 1 is 0.49 eV. The vertical EA of 0.49 eV can be simply estimated within Koopman's theorem, which is close to the experimental result [18]. Furthermore, using the SCF wave functions of H 2 CN − , the CI calculations predict a pole of 1 A 1 symmetry, which is 0.43 eV lower than the ground-state energy of H 2 CN.…”

“…However, this bound state can be formed in the experiment with electron EA of 0.511 eV [18]. The existence of a bound negative ion may seriously influence the cross sections at the corresponding symmetry 1 A 1 for the bound-state H 2 CN − .…”

“…Cowles et al [18] measured the ultraviolet photoelectron spectra of H 2 CN − and * Corresponding author: wangkd@htu.cn deduced the adiabatic electron affinity of the H 2 CN molecule to be 0.511 ± 0.008 eV. Eisfeld [16] calculated the adiabatic electron affinity of 0.5152 eV calculated with zero-point energy correction.…”

Description of the Methylene Amidogene Radical and Its Anion with an Economical Treatment of Correlation Effects Using Density Functional Theory Orbitals

“…Experimental findings systematically predict that these vibrational modes are located near 1336.6, 1725.4, 2820, 954.1, 912.8, and 3103.3 cm −1 , respectively. 3,4 Therefore, for H 2 CN, the comparison between our results and the experimental data demonstrates acceptable agreement especially for ν 2 , ν 4 , ν 5 , and ν 6 . The accordance of DFT-CASCI frequencies with various established methods such as MRCISD/AVQZ 13 and RCCSD(T)/AVQZ 14 as well as MRCISD+Q/cc-pcVQZ 12 and CCSD(T)/cc-pcVQZ 12 reflects that, for X ̃2B 2 , A ̃2B 1 , and B ̃2A 1 states, the approaches considered here characterize similarly the region of the minimum on the energy surface as that of our DFT-CASCI method.…”