The structure of Ar–N2O

Theoretical studies of infrared spectra for the N2-N2O complex: The tunneling effects of fundamental and combination bands

This study is a continuation of our previously published research for the N₂-N₂O complex [Journal of Chemical Physics 143 (2015) 154304], and focuses on predicting the quantum tunneling effects of infrared fundamental and combination bands. A new four-dimensional intermolecular potential energy surface (PES) was constructed for the vibrational excited state upon the N₂O ν₁ excitation at the same calculated level with the previous PES of ground state. Compared with the ground state, two equivalent T-shaped global minima are found to be slightly different in both structural parameters and binding energies. Based on the PESs of ground and vibrational excited states, the vibrational shift of infrared spectrum for the fundamental band in the N₂O ν₁ region is determined to be a blue shift of 1.29 cm^-1 for ¹⁴N₂-N₂O, which is in qualitative agreement with the experimentally observed value of 2.233 cm^-1 [Journal of Chemical Physics 140 (2014) 044332]. Furthermore, for the fundamental and disrotation bands, the calculated tunneling splitting is almost the same for the ground and vibrational excited states, so the tunneling effects cannot be observed for these bands using the infrared spectroscopic technique. Nevertheless for the infrared combination bands, our calculated results suggest that the tunneling effects for the torsion and twice disrotation bands are significantly larger, and the predicted infrared spectra display obvious differences for the different sub-states. If the sensitivity of infrared spectrometer is high enough, it is interesting to investigate the quantum tunneling effects experimentally.

Investigating the influence of intramolecular bond lengths on the intermolecular interaction of H2-AgCl complex: Binding energy, intermolecular vibrations, and isotope effects

In this paper, we performed a theoretical study on the influence of intramolecular bond lengths on the intermolecular interactions between H₂ and AgCl molecules. Using four sets of bond lengths for the monomers of H₂ and AgCl, four-dimensional intermolecular potential energy surfaces (PESs) were constructed from ab initio data points at the level of single and double excitation coupled cluster method with noniterative perturbation treatment of triple excitations. A T-shaped global minimum was found on the PES. Interestingly, both the binding energies and Ag-H₂ distances present a linear relationship with the intramolecular bond lengths of H₂-AgCl. The accuracy of these PESs was validated by the available spectroscopic data via the bound state calculations, and the predicted rotational transition frequencies can reproduce the experimental observations with a root-mean-squared error of 0.0003 cm^-1 based on the PES constructed with r(H-H) and r(Ag-Cl) fixed at 0.795 and 2.261 Å, respectively. The intermolecular vibrational modes were assigned unambiguously with a simple pattern by analyzing the wave functions. Isotope effects were also investigated by the theoretical calculations, and the results are in excellent agreement with the available spectroscopic data. The transition frequencies for the isotopolog D₂-AgCl are predicted with the accuracy of 0.3 MHz.

Structure and Abundance of Nitrous Oxide Complexes in Earth's Atmosphere

We have investigated the lowest energy structures and binding energies of a series of atmospherically relevant nitrous oxide (N2O) complexes using explicitly correlated coupled cluster theory. Specifically, we have considered complexes with nitrogen (N2-N2O), oxygen (O2-N2O), argon (Ar-N2O), and water (H2O-N2O). We have calculated rotational constants and harmonic vibrational frequencies for the complexes and the constituent monomers. Statistical mechanics was used to determine the thermodynamic parameters for complex formation as a function of temperature and pressure. These results, in combination with relevant atmospheric data, were used to estimate the abundance of N2O complexes in Earth's atmosphere as a function of altitude. We find that the abundance of N2O complexes in Earth's atmosphere is small but non-negligible, and we suggest that N2O complexes may contribute to absorption of terrestrial radiation and be relevant for understanding the atmospheric fate of N2O.

AB INITIO POTENTIAL ENERGY SURFACE AND PREDICTED ROVIBRATIONAL SPECTRA FOR THE Kr–N2O COMPLEX

The potential energy surface for the Kr – N 2 O complex is calculated using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] with a large basis set including midpoint bond functions. The interaction energies are obtained by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The CCSD(T) potential is found to have two minima corresponding to the T-shaped and linear Kr – ONN structures. The geometry for the T-shaped configuration is very close to the experimental results. The two-dimensional discrete variable representation method is applied to calculate the rovibrational energy levels with N 2 O at its ground and ν3 excited states. The calculated transition frequencies and spectroscopic constants are in good agreement with the observed values.

A three-dimensional ab initio potential energy surface and predicted infrared spectra for the He–N2O complex

We report a three-dimensional ab initio potential energy surface for He-N(2)O using a supermolecular method at the coupled-cluster singles and doubles with noniterative inclusion of connected triple level. Besides the intermolecular stretching and bending modes, we included the Q(3) normal mode for the nu(3) antisymmetric stretching vibration of N(2)O molecule in order to simulate the observed infrared spectra in the nu(3) region of N(2)O, especially to explain the frequency shift of the band origin in the infrared spectra. The harmonic oscillator approximation is used for the potential curve of the Q(3) mode of the isolate N(2)O molecule. The intermolecular potential energy surfaces are calculated for five potential-optimized discrete variable representation grid points of the Q(3) mode. The three-dimensional discrete variable representation method was employed to calculate the rovibrational states without separating the inter- and intramolecular nuclear motions. The calculated transition frequencies and line intensities of the rotational transitions in the nu(3) region of N(2)O for the van der Waals ground vibrational state are in good agreement with the observed infrared spectra. The calculated band shifts are found to be 0.1704 and 0.1551 cm(-1) for (4)He-N(2)O and (3)He-N(2)O, respectively, which agree well with the observed values of 0.2532 and 0.2170 cm(-1).

Intermolecular potential energy surface and rovibrational spectra of the He–N2O complex from ab initio calculations

We report an ab initio intermolecular potential energy surface calculation on the He-N(2)O complex with N(2)O at its ground state using a supermolecular approach. The calculation was performed at the coupled-cluster [CCSD(T)] level, with the full counterpoise correction for the basis set superposition error and a large basis set including midpoint bond functions. The CCSD(T) potential is found to have two minima corresponding to the T-shaped and linear He-ONN structures. The T-shaped minimum is the global minimum. The two-dimensional discrete variable representation method was employed to calculate the rovibrational energy levels for (4)He-N(2)O and (3)He-N(2)O with N(2)O at its ground and nu(3) excited states. The results indicate that the CCSD(T) potential supports five and four vibrational bound states for the (4)He-N(2)O and (3)He-N(2)O, respectively. Moreover, the calculations on the line intensities of the rotational transitions in the nu(3) region of N(2)O for the ground vibrational state shows that the (3)He-N(2)O spectrum is dominated by a-type transitions (DeltaK(a)=0), while the (4)He-N(2)O spectrum is contributed by both the a-type and b-type (DeltaK(a)=+/-1) transitions. The calculated transition frequencies and the intensities are in good agreement with the observed results.

The Rotational Spectra, Structure, Internal Dynamics, and Electric Dipole Moment of the Argon-Ketene van der Waals Complex

Pulsed-beam Fourier transform microwave spectroscopy was used to observe and assign the rotational spectra of the argon-ketene van der Waals complex. Tunneling of the hydrogen or deuterium atoms splits the a- and b-type rotational transitions of H(2)CCO-Ar, H(2)(13)CCO-Ar, H(2)C(13)CO-Ar, and D(2)CCO-Ar into two states. This internal motion appears to be quenched for HDCCO-Ar where only one state is observed. The spectra of all isotopomers were satisfactorily fit to a Watson asymmetric top Hamiltonian which gave A=10 447.9248(10) MHz, B=1918.0138(16) MHz, C=1606.7642(15) MHz, Delta(J)=16.0856(70) kHz, Delta(JK)=274.779(64) kHz, Delta(K)=-152.24(23) kHz, delta(J)=2.5313(18) kHz, delta(K)=209.85(82) kHz, and h(K)=1.562(64) kHz for the A(1) state of H(2)CCO-Ar. Electric dipole moment measurements determined &mgr;(a)=0.417(10)x10(-30) C m [0.125(3) D] and &mgr;(b)=4.566(7)x10(-30) C m [1.369(2) D] along the a and b principal axes of the A(1) state of the normal isotopomer. A least squares fit of principal moments of inertia, I(a) and I(c), of H(2)CCO-Ar, H(2)(13)CCO-Ar, and H(2)C(13)CO-Ar for the A(1) states give the argon-ketene center of mass separation, R(cm)=3.5868(3) Å, and the angle between the line connecting argon with the center of mass of ketene and the C=C=O axis, θ(cm)=96.4 degrees (2). The spectral data are consistent with a planar geometry with the argon atom tilted toward the carbonyl carbon of ketene by 6.4 degrees from a T-shaped configuration. Copyright 2001 Academic Press.

Study of the Rotational Spectrum of the Ne-N2O van der Waals Dimer with a Fourier Transform Microwave Spectrometer

Rotational spectra of six isotopomers of the van der Waals dimer Ne-N2O, namely 20Ne-14N14NO, 22Ne-14N14NO, 20Ne-14N15NO, 22Ne-14N15NO, 20Ne-15N14NO, and 22Ne-15N14NO, were measured in the frequency range between 5 and 18 GHz using a pulsed beam cavity Fourier transform microwave spectrometer. The spectra are those of prolate asymmetric rotors and are in accord with a T-shaped structure of the complex. Both a- and b-type transitions were measured. Nuclear quadrupole hyperfine patterns of the rotational transitions due to the 14N nuclei were observed and analyzed. The rotational and centrifugal distortion constants were determined, as well as the quadrupole coupling constants chiaa and chibb, for both terminal and central 14N nuclei. The distance from the center of mass of the N2O subunit to the Ne atom and the angle between this distance and the N2O axis were derived from the rotational constants. The structural parameters indicate that the Ne atom is on average closer to the O atom than to the terminal N atom. Copyright 1998 Academic Press.

High-Resolution Infrared Diode Laser Spectroscopy of Ne-N2O, Kr-N2O, and Xe-N2O

The rotationally resolved spectra of the van der Waals complexes Ne-N2O, Kr-N2O, and Xe-N2O have been investigated in the region of the nu3 N2O monomer vibrational band using a diode laser absorption spectrometer that is incorporated with a multipass cell and a pulsed jet. The spectra of these three complexes are completely analyzed using a normal asymmetric rotor Hamiltonian, and the effective molecular constants are accurately determined for both the ground and the excited vibrational states. These results show that, like Ar-N2O, the complexes have a T-shaped configuration in which the rare gas atom prefers to lie near to the oxygen side of N2O. The band origins of Rg-N2O (Rg = Ne, Ar, Kr, and Xe) are observed to shift by 0.36125, 0.15038, -0.10131, and -0.49066 cm-1 from that of the monomer, respectively. These band origin shifts are well explained by a simple model for the intermolecular potential. Copyright 1998 Academic Press.

Fourier-Transform Microwave Spectroscopy of the Argon-Diacetylene van der Waals Complex

The rotational spectrum of the argon-diacetylene van der Waals complex, produced in a supersonic molecular beam at 1 K, has been observed with a Fourier-transform microwave spectrometer. We observed 22 a-type rotational transitions with Ka up to 3. Three rotational constants, five centrifugal distortion constants, and one higher-order centrifugal distortion constant were determined precisely by least-squares analysis. The complex is shown to have a planer T-shaped structure with C2v symmetry. The structural analysis provides that the Ar atom is located 3.68 A from the center of mass of diacetylene. Force constants for the van der Waals vibrations were determined from the centrifugal distortion constants. It has been found that this complex has a much steeper and more harmonic intermolecular potential than the argon-acetylene complex. Copyright 1997 Academic Press. Copyright 1997Academic Press