(a) A two-dimensional laser induced fluorescence (2D-LIF) image of a supersonic free jet expansion of fluorobenzene (FB) in argon in the region of the FB transition. The laser wavenumber is along the horizontal axis, while the dispersed fluorescence wavenumber is along the vertical axis. The image shows features due to FB, FB-Ar, and FB-Ar2. The features above and below the intense FB feature at an absorption photon energy of 37 813.8 cm−1 are grating ghosts. (b) The image shown in (a) with enhanced 2D-LIF scans of key regions inserted to better reveal weaker features of the image. The intensities of the inserted sections are increased by the factor indicated on the enhanced section.
The LIF spectrum of FB-Ar extracted by vertically integrating a horizontal slice taken from Fig. 1. The slice encompasses FB-Ar van der Waals bands while minimising contributions from other species. The lower trace is from Fig. 1(a), while the ×20 spectra are generated from the enhanced 2D-LIF segments in Fig. 1(b). The feature between +21 and +25 cm−1 is due to a grating ghost associated with the origin band of FB.
The 2D-LIF image and corresponding dispersed fluorescence spectrum arising from scanning the laser over the band of FB-Ar and monitoring dispersed fluorescence in the region near . Because the dispersed fluorescence spectrum is the focus here, the image is displayed with the laser wavenumber on the vertical axis and dispersed fluorescence wavenumber along the horizontal axis. The dispersed fluorescence spectrum is extracted by integrating the image along the laser wavenumber axis.
The LIF contour for the FB-Ar band extracted by integrating only the fluorescence band. A low laser fluence (known to be in the linear absorption regime) was used to eliminate saturation effects. The best-fit contour and rotational constants are also shown (see text). The x axis represents displacement from the band origin. The band maximum is shifted approximately +0.1 cm−1. All rotational constants associated with the fit are given in Table II.
The 2D-LIF image and corresponding dispersed fluorescence spectrum arising from scanning the laser over the band of FB-Ar2 and monitoring dispersed fluorescence in the region near . The image is displayed with the laser wavenumber on the vertical axis and dispersed fluorescence wavenumber along the horizontal axis. The dispersed fluorescence spectrum is extracted by integrating the image along the laser wavenumber axis.
The LIF contour for the FB-Ar2 band (solid line) extracted by vertically integrating a horizontal slice taken from Fig. 1(b). The predicted contour is also shown as a dashed line (see text). For the purpose of comparison, the peak positions of the two spectra have been aligned. The x axis represents the shift from the peak position. The rotational constants associated with the predicted contour are shown in Table V.
A summary of the transitions associated with FB, FB-Ar, and FB-Ar2 observed in the 2D-LIF images.
FB-Ar rotational constants determined from experimental and ab initio studies. The previously reported values are provided for comparison. The S0 values, needed to calculate the rotational contour, are also given.
The FB-Ar geometry calculated using various methods. R is the distance from the FB centre of mass (CoM) to the Ar atom; θ is the angle between the normal to the plane of the FB molecule and the line joining the Ar atom and the FB CoM; θ lies in the mirror plane of the complex. α is the average libration/rocking angle associated with zero point motion of the FB molecule within the complex (see text).
A comparison between the observed rotational constants for M-Rg2 trimers and those predicted from the M-Rg geometry determined from the M and M-Rg rotational constants.
Predicted FB-Ar2 rotational constants and the difference between the S0 and S1 constants (Δ). The constants are given in units of cm‑1.
A comparison between the experimentally observed S0 vibrational levels and those calculated by ab initio methods.
A comparison of the S1 van der Waals vibrational levels observed and their relative intensities with those calculated. Previously reported experimental values are included.
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