Accurate determination of the structure of 1,3,5-trifluorobenzene by femtosecond rotational Raman coherence spectroscopy and ab initio calculations

Rotational constants and structure of para-difluorobenzene determined by femtosecond Raman coherence spectroscopy: A new transient type

“…The fitted ratio is 1.04 ± 0.06, which is in good agreement with the CCSD(T) calculated ratios of 0.996-1.051 given in Table III. There is practically no collisional dephasing in the supersonic jet, as we have shown experimentally for the symmetrictop molecules cyclohexane, trifluorobenzene, and hexafluorobenzene. 2,3,43 Due to the irregular spacing of the transition frequencies in asymmetric-top molecules, their RCS transients decays more rapidly with time than compared to symmetrictop molecules; this is already quite marked given the sizable asymmetry of p-DFB with κ = −0.87. Thus, the RCS transient of hexafluorobenzene shows observable recurrences up to t ∼ 5000 ps delay, 3 but the last observable recurrences of p-DFB lie at t ∼ 1375 ps, see Figure 3(i).…”

“…2,20,21 Briefly, three parallel laser beams from an amplified Ti:Sapphire laser system provide the ∼75 fs pulses at 800 nm employed for the stimulated Raman pump, dump, and probe steps. The stimulated Raman polarization induced by the pump/dump steps at time zero is detected by the DFWM signal generated from the time-delayed probe pulse.…”

“…ab initio methods to determine a semiexperimental structure by linear basis-set extrapolation, as has been described earlier for symmetric-top molecules for which only one rotational constant is experimentally accessible. [1][2][3]17,19,20,48 In short, a structural parameter r (bond length, bond angle) is calculated using highly correlated ab initio calculations, e.g., the CCSD(T) method using a systematic series of basis sets, e.g. the Dunning correlation-consistent weighted core-valence polarized basis sets series cc-pwCVXZ, where X = 2, 3, .…”

“…Using femtosecond (fs) Raman a) leutwyler@iac.unibe.ch rotational coherence spectroscopy (RCS), the Bern group has previously determined rotational and centrifugal distortion constants for the symmetric tops 1,3,5-trifluorobenzene (TFB) and hexafluorobenzene (HFB) by fitting the experimental RCS transients. 2,3 Combining these results with CCSD(T) correlated calculations allowed to determine semiexperimental C-F and C-C bond lengths. [1][2][3] Para-difluorobenzene (p-DFB), shown in Figure 1, is also nonpolar.…”

“…2,3 Combining these results with CCSD(T) correlated calculations allowed to determine semiexperimental C-F and C-C bond lengths. [1][2][3] Para-difluorobenzene (p-DFB), shown in Figure 1, is also nonpolar. However, compared to the treatments of the symmetric top molecules TFB and HFB, the asymmetric-top Raman RCS simulations are significantly more involved: First, the asymmetric-top rotational eigenfunctions and energy eigenvalues E(J, K 1 , K −1 ) must be computed numerically, in contrast to symmetric tops whose rotational level energies can be expressed analytically.…”