Photoelectron spectroscopy of CN−, NCO−, and NCS−

The 266 nm photoelectron spectra of CN−, NCO−, and NCS− have been recorded with a pulsed time-of-flight photoelectron spectrometer. The photoelectron spectrum of CN− has also been recorded at 213 nm revealing transitions to the A 2Π state as well as the ground X 2Σ+ state of the CN radical. The following adiabatic electron affinities (EAs) are determined: EA(CN)=3.862±0.004 eV, EA(NCO)=3.609±0.005 eV, and EA(NCS)=3.537±0.005 eV. The adiabatic electron affinity of cyanide is in disagreement with the currently accepted literature value. Our measurement of the electron affinity of NCS confirms recent theoretical estimates that dispute the literature experimental value. By Franck–Condon analysis of the vibrational progressions observed in each spectrum, the change in bond lengths between anion and neutral are also determined. For NCO− this yields R0(C–N)=1.17±0.01 Å and R0(C–O)=1.26±0.01 Å, and for CN− the equilibrium bond length is found to be Re(C–N)=1.177±0.004 Å. The gas phase fundamental for CN− is determined for the first time: ν=2035±40 cm−1.