skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Millimeter-wave Spectroscopy of the Chlorine Isotopologues of 2-Chloropyridine and Twenty-three of their Vibrationally Excited States
Title: Millimeter-wave Spectroscopy of the Chlorine Isotopologues of 2-Chloropyridine and Twenty-three of their Vibrationally Excited States
A combined total of 25 vibrational states of 2-chloropyridine (C5H4NCl, la = 3.07 D, lb = 1.70 D), including states for both chlorine isotopologues, have been least-squares fit to sextic, A-reduced Hamiltonians with low error (<0.05 MHz). In total, over 22,500 transition frequencies were measured in the 135–375 GHz frequency region. The technique of fixing undeterminable distortion constants to the corresponding values of the ground vibrational state for fundamental states and to extrapolated values for overtone and combination states was employed. The experimentally determined rotational, centrifugal distortion, and vibration-rotation interaction constants are reasonably well-predicted by computational methods (B3LYP/6-311+G(2d,p)). For the chlorine isotopologues, the changes in rotational and quartic distortion constants upon vibrational excitation are quite similar, indicating that it is possible to estimate the constants of a lower-abundance isotopologue’s excited vibrational state using the change in constant observed in the higher-abundance isotopologue. The changes in rotational and quartic distortion constants upon vibrational excitation are also quite similar between analogous vibrational states of 2-chloropyridine and chloropyrazine, despite their differences in molecular composition.  more » « less
Award ID(s):
1664912
PAR ID:
10190793
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Journal of molecular spectroscopy
Volume:
365
ISSN:
0022-2852
Page Range / eLocation ID:
111206
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; (, The Journal of Chemical Physics)
    In this work, we present the spectral analysis of 1 H- and 2 H-1,2,3-triazole vibrationally excited states alongside provisional and practical computational predictions of the excited-state quartic centrifugal distortion constants. The low-energy fundamental vibrational states of 1 H-1,2,3-triazole and five of its deuteriated isotopologues ([1- 2 H]-, [4- 2 H]-, [5- 2 H]-, [4,5- 2 H]-, and [1,4,5- 2 H]-1 H-1,2,3-triazole), as well as those of 2 H-1,2,3-triazole and five of its deuteriated isotopologues ([2- 2 H]-, [4- 2 H]-, [2,4- 2 H]-, [4,5- 2 H]-, and [2,4,5- 2 H]-2 H-1,2,3-triazole), are studied using millimeter-wave spectroscopy in the 130–375 GHz frequency region. The normal and [2- 2 H]-isotopologues of 2 H-1,2,3-triazole are also analyzed using high-resolution infrared spectroscopy, determining the precise energies of three of their low-energy fundamental states. The resulting spectroscopic constants for each of the vibrationally excited states are reported for the first time. Coupled-cluster vibration–rotation interaction constants are compared with each of their experimentally determined values, often showing agreement within 500 kHz. Newly available coupled-cluster predictions of the excited-state quartic centrifugal distortion constants based on fourth-order vibrational perturbation theory are benchmarked using a large number of the 1,2,3-triazole tautomer isotopologues and vibrationally excited states studied. 
    more » « less
  2. ; ; ; ; (, Journal of molecular spectroscopy)
    The measurement of over 24,000 new rotational transitions of chloropyrazine (C4H3N2Cl, la = 1.55 D, lb = 0.14 D) in the 130–375 GHz frequency region enabled the assignments of the rotational spectra for the ground vibrational states of the [35Cl]- and [37Cl]-isotopologues and a combined total of 22 low-energy excited vibrational states. These vibrational states have been fit to sextic A-reduced Hamiltonians with low error (<0.05 MHz). These data allow for precise determination of the vibration-rotation interaction constants for the six lowest-energy fundamental vibrational modes (m24, m17, m23, m16, m22, and m15) of the [35Cl]-isotopologue and the four lowest-energy fundamental vibrational modes (m24, m17, m23, and m16) of the [37Cl]-isotopologue. In addition, many combination and overtone states were observed, bringing the total number of excited states to seventeen for the [35Cl]-isotopologue and five for the [37Cl]-isotopologue. The spectroscopic constants for the ground state, m24, and m17 for each isotopologue are very well determined (Nlines > 1400 for each least-squares fit). The vibration-rotation interaction constants experimentally determined for all observed fundamentals are generally in quite close agreement with their predicted (B3LYP/6-311+G(2d,p)) values. 
    more » « less
  3. ; ; (, Physical Chemistry Chemical Physics)
    High-level rovibrational characterization of methanediol, the simplest geminal diol, using state-of-the-art, purely ab initio techniques unequivocally confirms previously reported gas phase preparation of this simplest geminal diol in its C 2 conformation. The F12-TZ-cCR and F12-DZ-cCR quartic force fields (QFFs) utilized in this work are among the largest coupled cluster-based anharmonic frequencies computed to date, and they match the experimental band origins of the spectral features in the 980–1100 cm −1 range to within 3 cm −1 , representing a significant improvement over previous studies. The simulated spectrum also matches the experimental spectrum in the strong Q branch feature and qualitative shape of the 980–1100 cm −1 region. Additionally, the full set of rotational constants, anharmonic vibrational frequencies, and quartic and sextic distortion constants are provided for both the lowest energy C 2 conformer as well as the slightly higher C s conformer. Several vibrational modes have intensities of 60 km mol −1 or higher, facilitating potential astronomical or atmospheric detection of methanediol or further identification in laboratory work especially now that gas phase synthesis of this molecule has been established. 
    more » « less
  4. (, The Journal of chemical physics)
    The fine and hyperfine interactions in PbF have been studied using the laser-induced fluorescence (LIF) spectroscopy method. Cold PbF molecular beam was produced by laser-ablating a Pb rod under jet-cooled conditions, followed by the reaction with SF6. The LIF excitation spectrum of the (0, 0) band in the B2Σ+–X2Π1/2 system of the 208PbF, 207PbF, and 206PbF isotopologues has been recorded with rotational, fine structure, and hyperfine-structure resolution. Transitions in the LIF spectrum were assigned and combined with the previous X2Π3/2–X2Π1/2 emission spectrum in the near-infrared region [Ziebarth et al., J. Mol. Spectrosc. 191, 108–116 (1998)] and the X2Π1/2 state pure rotational spectrum of PbF [Mawhorter et al., Phys. Rev. A 84, 022508 (2011)] in a global fit to derive the rotational, spin–orbit, spin–rotation, and hyperfine interaction parameters of the ground (X2Π1/2) and the excited (B2Σ+) electronic states. Molecular constants determined in the present work are compared with previously reported values. Particularly, the significance of the hyperfine parameters, A⊥ and A‖, of 207Pb is discussed. 
    more » « less
  5. ; ; (, Molecules)
    New high-level ab initio quartic force field (QFF) methods are explored which provide spectroscopic data for the electronically excited states of the carbon monoxide, water, and formaldehyde cations, sentinel species for expanded, recent cometary spectral analysis. QFFs based on equation-of-motion ionization potential (EOM-IP) with a complete basis set extrapolation and core correlation corrections provide assignment for the fundamental vibrational frequencies of the A˜2B1 and B˜2A1 states of the formaldehyde cation; only three of these frequencies have experimental assignment available. Rotational constants corresponding to these vibrational excitations are also provided for the first time for all electronically excited states of both of these molecules. EOM-IP-CCSDT/CcC computations support tentative re-assignment of the ν1 and ν3 frequencies of the B˜2B2 state of the water cation to approximately 2409.3 cm−1 and 1785.7 cm−1, respectively, due to significant disagreement between experimental assignment and all levels of theory computed herein, as well as work by previous authors. The EOM-IP-CCSDT/CcC QFF achieves agreement to within 12 cm−1 for the fundamental vibrational frequencies of the electronic ground state of the water cation compared to experimental values and to the high-level theoretical benchmarks for variationally-accessible states. Less costly EOM-IP based approaches are also explored using approximate triples coupled cluster methods, as well as electronically excited state QFFs based on EOM-CC3 and the previous (T)+EOM approach. The novel data, including vibrationally corrected rotational constants for all states studied herein, provided by these computations should be useful in clarifying comet evolution or other remote sensing applications in addition to fundamental spectroscopy. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email