High Resolution Infrared Absorption Spectroscopy Of Several Atmospheric Molecular Complexes

The earth’s atmosphere is an important part of the earth’s ecological environment,which provides an important guarantee for the reproduction of life.With the industrial revolution and increase of population,the atmospheric trace gases of oxynitride,oxysulfide,oxycarbide have a serious impact on global ecological environment and climate change.Van der Waals interaction plays a key role in the fields of physics,chemistry and life medicine such as phase transition,aerosol formation and protein synthesis.The absorption spectra of van der Waals complexes containing oxynitride,oxysulfide,oxycarbide and water is an important means to study the molecular structure,kinetic characteristics,reaction paths and interactions.It is also an important basis to study earth’s atmosphere.In this dissertation,high resolution infrared absorption spectra of several atmospheric molecular complexes are investigated using an external cavity quantum cascade laser(ECQCL)combined with a supersonic slit jet expansion.The main results are as follows:1.The rovibrational spectra of Ar-N2O and nonpolar(N2O)2 are measured in 2v2 overtone band region of N2O.Accurate molecular constants are determined by a weighted leastsquares fitting using a standard Watson A-reduced asymmetric rotor Hamiltonian.Quantum chemical calculations of vibrational frequencies and infrared intensities of these two complexes are performed at the MP2/aug-cc-pvtz level of theory.The ArN2O vibrational band is assigned as an overtone band of the bending mode.The nonpoalr(N2O)2 vibrational band is assigned as a combination band of the intramolecular symmetric and anti-symmetric in-plane bending modes.The bandorigin is located at v0=1168.177584(76)cm-1 for Ar-N2O and v0=1165.218580(54)cm-1 for nonpolar(N2O)2,which shows a blue-shift by 0.0451 cm-1 for Ar-N2O and a red-shift by 2.9139 cm-1 for nonpolar(N2O)2 compared with that of the N2O(0200)(0000)band,respectively.2.One vibrational band for Ar-SO2 and two for(SO2)2 are measured in v1 stretching region of SO2.The tunneling splitting is resolved in the Ar-SO2 vibrational band.The observed spectra are analyzed together with previous radio frequency and microwave spectra by a fitting,yielding precise molecular constants in both the ground and excited vibrational states for these two complexes.The band origins of(SO2)2 are determined to be 1150.30319(13)cm-1 and 1153.40911(10)cm-1,which is shifted from that of the SO2 v1 band by about-1.41 cm-1 and+1.70 cm-1,respectively.The vibrational energies of the two tunneling components of Ar-SO2 are determined to be 1151.61315(11)cm-1 and 1151.64840(11)cm-1.The tunneling splitting of Ar-SO2 in the excited vibrational state is 1056.7(34)MHz,which bigger than that in the ground state,indicating a decrease of the tunneling barrier upon excitation of the SO2 symmetric stretching vibration.3.The rovibrational spectra of N2-SO2 and CO-SO2 are measured in v1 stretching region of SO2.The observed transitions are of c-type for both complexes.The observed spectra are assigned and fitted by a weighted least-squares fitting using a standard Watson S-reduced asymmetric top Hamiltonian,yielding accurate rotation constants and centrifugal distortion constants in the excited vibrational state.The band origins of N2-SO2 and OC-SO2 are determined to be 1152.574299(63)cm-1 and 1153.141389(45)cm-1,which shows a blue-shift from that of the monomer by about 0.86 cm-1 and 1.43 cm-1,respectively.4.Four new rovibrational subbands of Ar-D2O are measured in v2 bending region of D2O,namely ∑(000,v2=1)←∑(111),∑(000,v2=1)←∏(111),∑(101,v2=1)←∏(110)and ∑(101,v2=1)←∏(101).The observed transitions together with the previously reported pure rotational spectra having the common lower vibrational sub-states are analyzed by a weighted least-squares fitting using a pseudo-diatomic effective Hamiltonian.The band origin of Ar-D2O in the D2O v2 bending mode region is located at v0=1177.92144(13)cm-1,which shows a red shift about 0.458 cm-1 compared with the head of D2O monomer.The experimental vibrational substate energy is compared with the theoretical value based on a four-dimensional intermolecular potential energy surface to verify the accuracy of the theoretical calculation.