Photoelectron spectroscopic study of 2-naphthylnitrene and its thermal rearrangement to cyanoindenes

2-Cyanoindene has recently been identified in the interstellar medium, however current models cannot fully account for its formation pathways. Herein, we identify and characterize 2-naphthylnitrene, which is prone to rearrange to 2- and 3-cyanoindene, in the gas phase using photoion mass-selective threshold photoelectron spectroscopy (ms-TPES). The adiabatic ionization energies (AIE) of triplet nitrene (3A '') to the radical cation in its lowest-energy doublet X +(2A ') and quartet a+(4A ') electronic states were determined to be 7.72 +/- 0.02 and 8.64 +/- 0.02 eV, respectively, leading to a doublet-quartet energy splitting (Delta ED-Q) of 0.92 eV (88.8 kJ mol-1). A ring-contraction mechanism yields 3-cyanoindene, which is selectively formed under mild pyrolysis conditions (800 K), while the lowest-energy isomer, 2-cyanoindene, is also observed under harsh pyrolysis conditions at 1100 K. The isomer-selective assignment was rationalized by Franck-Condon spectral modeling and by measuring the AIEs at 8.64 +/- 0.02 and 8.70 +/- 0.02 eV for 2- and 3-cyanoindene, respectively, in good agreement with quantum chemical calculations. Unveiling new spectroscopic and mechanistic insights into interstellar chemistry: photoionization of triplet 2-napthylnitrene and its thermal rearrangement to 2- and 3-cyanoindene, as monitored with threshold photoelectron spectroscopy.