Note
New measurements and global analysis of rotational spectra of Cl-, Br-, and I-benzene: Spectroscopic constants and electric dipole moments

https://doi.org/10.1016/j.jms.2007.09.010Get rights and content

Abstract

The data available from rotational spectroscopy for chlorobenzene, bromobenzene, and iodobenzene have been extended by new measurements in the mm-wave region and in supersonic expansion in the cm-wave region. All available ground state measurements have been combined in global fits to derive precise rotational, centrifugal, and nuclear quadrupole coupling constants for the molecules. Rotational transitions in first excited states of the lowest frequency normal modes in bromobenzene and iodobenzene have been assigned and fitted. The values of electric dipole moments for 35Cl-, 79Br-, 81Br-, and I-benzene have been determined from Stark effect measurements on selected hyperfine components in the supersonic expansion spectrum, and are compared with values for several other series of monohalogen molecules.

Introduction

The first studies of the fundamental single halogen benzene derivatives by rotational spectroscopy were carried out over 40 years ago, Refs. [1], [2], [3], [4] for F-, Cl-, Br-, and I-benzene, respectively. Many further investigations have been made since then including room-temperature cm-wave studies of hyperfine resolved transitions for the three heaviest molecules [5], [6]. Nevertheless, it is only for fluorobenzene [7] that the high-resolution results from contemporary supersonic expansion Fourier transform microwave spectroscopy (FTMW) have been combined with high-J measurements in the mm-wave (MMW) rotational spectrum. For chlorobenzene some MMW [8], but not FTMW results are available, whereas for bromobenzene [9], [10] and iodobenzene [10] the FTMW and not the MMW spectrum has been studied. We presently systematically extend the experimental information to allow determination of spectroscopic constants for all monohalogenobenzenes at the level of precision allowed by contemporary rotational spectroscopy.

Section snippets

Experimental details

All measurements were carried out on the two rotational spectrometers in Warsaw, the supersonic expansion FTMW spectrometer [11] and the broadband MMW spectrometer [12]. Measurements for chlorobenzene were made up to 312 GHz, while for bromo- and iodobenzene up to 220 GHz, corresponding to maximum values of J″ of 125, 129, and 164, respectively, for the three molecules. Stark effect measurements were carried out using the electrode arrangement designed for obtaining a uniform electric field under

Rotational spectrum

The high-J rotational spectra of the studied monohalogenobenzene molecules show features typical of planar molecules, as illustrated for iodobenzene in Fig. 1. The properties of the type-II+ bands visible in this spectrum are well known [16], [17] and allow ready assignment of the mm-wave spectrum, as has previously been used to advantage for chlorobenzene [8] and fluorobenzene [7]. The measurements of the mm-wave rotational spectrum for chlorobenzene are presently extended up to 314 GHz, while

Excited vibrational states

All of the studied molecules have several low-frequency vibrational modes, so that in the mm-wave spectrum the prominent high-J band for the ground state is accompanied by several vibrational satellite bands, as visible for iodobenzene in Fig. 1. The lowest frequency normal modes are due to the motion of the halogen relative to the phenyl ring and are: the out-of-plane bend of the halogen in relation to the ring, ν30(B2), the corresponding in-plane bend, ν24 (B1), and the CX stretch, ν11(A1).

Electric dipole moments

Electric dipole moment for each molecule was determined by performing Stark shift measurements on many different Stark lobes belonging to several hyperfine components of rotational transitions with low values of Ka. The results are summarised in Table 3 and the primary data files are in Table S9. The exact agreement between the dipole moment values derived for the two isotopologues of bromobenzene confirms self-consistency of the experimental method. The current results are compared in Fig. 2

Conclusion

The present work reports the hitherto most precise rotational, centrifugal distortion, and nuclear quadrupole splitting constants for the ground states of chlorobenzene, bromobenzene and iodobenzene. The new values have been derived by combining new measurements of rotational transitions with the use of global fits to all data available from rotational spectroscopy. The ground state estimates of the ratios of nuclear quadrupole moments for the isotopic nuclei given by χaa(35Cl)/χaa(37Cl) = 

Acknowledgment

Financial support from the Institute of Physics of the Polish Academy of Sciences is gratefully acknowledged.

References (34)

  • W. Caminati et al.

    Chem. Phys. Lett.

    (1971)
  • A.M. Mirri et al.

    Chem. Phys. Lett.

    (1971)
  • Z. Kisiel et al.

    J. Mol. Spectrosc.

    (2005)
  • Z. Kisiel

    J. Mol. Spectrosc.

    (1990)
  • S.A. Peebles et al.

    J. Mol. Struct.

    (2003)
  • K.C. Etchison et al.

    J. Mol. Spectrosc.

    (2007)
  • I. Medvedev et al.

    J. Mol. Spectrosc.

    (2004)
  • Z. Kisiel et al.

    Chem. Phys. Lett.

    (2000)
  • Z. Kisiel et al.

    J. Mol. Spectrosc.

    (2001)
  • Z. Kisiel et al.

    J. Mol. Spectrosc.

    (1996)
  • Z. Kisiel et al.

    J. Mol. Spectrosc.

    (1996)
  • H.M. Pickett

    J. Mol. Spectrosc.

    (1991)
  • F.A. van Dijk et al.

    Chem. Phys. Lett.

    (1970)
  • M.D. Marshall et al.

    J. Mol. Spectrosc.

    (1980)
  • G. Wlodarczak et al.

    J. Mol. Spectrosc.

    (1985)
  • M. Ieki et al.

    J. Mol. Spectrosc.

    (1978)
  • J. Gadhi et al.

    Chem. Phys. Lett.

    (1989)
  • Cited by (25)

    • Millimeter-wave spectroscopy of the chlorine isotopologues of 2-chloropyridine and twenty-three of their vibrationally excited states

      2019, Journal of Molecular Spectroscopy
      Citation Excerpt :

      The current work extends the frequency range observed for 2-chloropyridine to 375 GHz. In addition to the chloropyridines, the rotational spectra of several other analogous chlorinated aromatic compounds have been previously reported (chlorobenzene [22,23], 2-chloropyrimidine [24], and chloropyrazine [25]; Fig. 2). Of the previous studies of the chloroarenes, those of chloropyrazine and 2-chloropyrimidine provide the most detailed analysis of the vibrationally excited states and provide meaningful comparisons to the vibrationally excited states observed in the current work.

    • Millimeter-wave spectroscopy of the chlorine isotopologues of chloropyrazine and twenty-two of their vibrationally excited states

      2019, Journal of Molecular Spectroscopy
      Citation Excerpt :

      State D is very likely ν15, the B1 out-of-plane ring deformation mode without significant chlorine atom motion. The observation of these states, particularly the modes corresponding to the out-of-plane ring deformation with chlorine motion and the in-plane bend of σC-Cl, is consistent with those observed in studies of other monosubstituted haloarenes [2,19]. Two states lower in energy (ν9 and ν16 + ν24), and thus more intense than ν15, were not identified in the previous work [6].

    View all citing articles on Scopus
    View full text