Spectroscopic Characterization of Hydrogen‐Bonded 2,7‐Diazaindole‐Ammonia Complex: Laser Spectroscopic Investigations of Isolated Gas Phase Molecules

We present the vibrationally resolved two-color resonant two-photon ionization (R2PI), laser induced fluorescence (LIF), single vibronic level fluorescence (SVLF), and isomer-selective fluorescence dip infrared spectroscopy (FDIR) of 2,7-diazaindole-ammonia (27DAI-NH₃) complex seeded in a supersonic jet. The vibrational band due to internal translation of ammonia molecule in the complex appeared at 169 and 182 cm^-1 in the ground and excited state, respectively, suggesting a stronger hydrogen bonding interaction upon electronic excitation.The ground state structure of the complex was obtained using the FDIR spectrum with four bands observed at 3240, 3304, 3403, and 3433 cm^-1, which showed a good agreement with the vibrational frequencies of the most stable structure.- The ν_N(1)─H frequency of the complex at 3240 cm^-1 showed a significant red shift of 283 cm^-1 to that of the 27DAI monomer, suggesting a strong N(1)─H⋯N interaction in the complex. Further, the v_N(1)─H value of 27DAI-NH₃ complex provided a blue shift of 15 cm^-1 compared to 7AI-NH₃ complex, implying a weakening of the N(1)─H⋯N hydrogen bonding interaction due to N(2) insertion. The current investigation also revealed that in the ground electronic state, the N(2) insertion makes 27DAI molecule a weaker hydrogen bond donor and acceptor compared to that of the 7AI molecule.