Mid-infrared Laser Spectroscopy Of Open-shell Van Der Waals Complexes Containing Nitric Oxide

Intermolecular interactions play a key role in the fields of physics,chemistry,biology,life science and so on.The research of infrared spectra,structure and dynamics of van der Waals complexes is one of the important methods to understand the nature of intermolecular interactions.Van der Waals complexes containing nitric oxide（NO）are the prototypes to investigate the noncovalent interactions between open-shell molecules and closed-shell molecules or atoms.In this thesis,the high-resolution mid-infrared absorption spectroscopy based on continuous distributed feed-back quantum cascade lasers（CW-DFB-QCLs）and supersonic molecular beam are used to measure the rovibrational spectra of four NO-X（X=Ar,Ne,N₂O,CO₂）open shell complexes in the N-O stretching fundamental band region（～5.3μm）.The main results are listed as follows:1.Ar-NO（X²Π）complex.Five P-subbands,namely,P’←P":1/2←3/2,1/2←1/2,3/2←1/2,5/2←3/2 and 7/2←5/2,are observed.The hyperfine structure due to the nuclei spin of 14N（I=1）can be partially resolved in the P’←P":1/2←3/2,1/2←1/2 and 3/2←1/2 subbands.The fine and hyperfine structures of the infrared and microwave spectra are analyzed together with a semi-rigid rotor Hamiltonian for a planar open-shell complex,and molecular parameters are determined precisely.A linear J-dependence of the angle between the inertial a-axis of the complex and the intramolecular axis of the NO subunit,θ=θ0+Δθ（J+0.5）is introduced in order to model the strong structural relaxation effect in the P=1/2 state.Moreover,the observed infrared spectrum is also analyzed using Meyer’s empirical Hamiltonian.A series of quantitative parameters related to the intermolecular interactions are derived.2.Ne-NO（X²Π）complex.Three P-subbands（P’←P":1/2←1/2,3/2←1/2,5/2←3/2）are observed.The hyperfine structure due to the nuclei spin of 14N（I=1）is partially resolved in the P’←P":1/2←1/2 and 3/2<-1/2 subbands.The observed mid-infrared spectrum of Ne-NO（X²Π）together with the previously reported microwave spectrum is analyzed using a modified semirigid asymmetric rotor Hamiltonian for a planar open-shell complex.Accurate molecular constant are determined.The band origin is located at 1876.0606（97）cm-1 and has a blue-shift from that of the NO monomer by about 0.0888 cm-1,which is about half of the value in the first overtone region.3.NO（X²Π）-N₂O complex.Geometry optimizations of the complex with restricted to a planar configuration are calculated at the RCCSD（T）/aug-cc-pVTZ level of theory and the N atom of NO is found to point to the central N atom of N₂O at the minimum of the 2A" state.A total of 321 transitions with J≤16.5 and P ≤ 5.5 are included in the non-linear least-squares fitting.Accurate molecular constant are determined.The band-origin of the complex is located at 1 879.520（50）cm-1,which is blue-shifted by about 3.548 cm-1 from that of the NO fundamental band.The vibrationally averaged 2A’-2A" energy separation（Renner-Teller parameter）is determined to be ε=144.56（95）cm-1 for the ground state,indicating the electronic orbital angular momentum of NO is partially quenched upon complexation with N₂O.4.NO（X²Π）-CO₂ complex.Geometry optimizations at restricted configurations with a Cs symmetry are carried out at the RCCSD（T）/aug-cc-pvtz level of theory.This complex has a T-shaped structure at the global minimum on the ground electronic state（2A"）,with the N atom of NO pointing to the C atom of CO₂.Half of the possible rovibrational levels are missing due to spin statistics of the two identical 16O nuclei（I=0）in the CO₂ subunit of the complex.A total of 234 transitions with J≤17.5 and P≤5.5 are included in the non-linear least-squares fitting.The band-origin of the complex is located at 1880.4518（67）cm-1,which is blue-shifted from that of the NO monomer by about 4.48 cm-1.The quenching parameter is determined to be ε=129.80（50）cm-1 for the ground state,indicating the electronic orbital angular momentum of NO is partially quenched upon complexation with CO₂.