High-resolution UV spectrum of the benzene—N2 van der Waals complex

The rotationally resolved spectrum of the 610 band of the S1 ← S0 electronic transition of the benzene—N2 van der Waals complex has been recorded and 119 transitions assigned. The C6H6·N2 complex, produced in a pulsed molecular beam, was detected by mass-selected two-photon two-colour ionization employing a high-resolution (ΔνUV = 100 MHz, fwhm) pulsed-amplified cw laser for the resonant intermediate excitation. The observed rotational structure is that of a rigid symmetric top with weaker additional rotational transitions most likely arising from the free internal rotation of the N2 in the plane parallel to the benzene ring. The N2 is located parallel to the benzene ring at a distance of 3.50 Å; this decreases by 45 mÅ in the excited electronic state

Pulsed Doppler-free two-photon spectroscopy of polyatomic molecules

Doppler-free two-photon electronic spectra of a large polyatomic molecule are recorded for the first time with pulsed laser radiation of near Fourier-transform limited bandwidth (Δvnot, vert, similar100 MHz). The resolution obtained is sufficient to resolve individual rotational lines. Due to the high density of these rotational transitions a strong Doppler-broadened background is observed, which is, however, subtantially reduced by suitable choice of photon polarizations. Different vibronic bands of benzene (C6H6) are investigated and very accurate rotational constants are found

Heterogeneous perturbations in the Doppler-free S1 ← S0 two-photon spectrum of benzene: Evidence for intrastate coupling

Rotational perturbations are identified in Doppler-free two-photon spectra of the 1410 and 1410110 vibronic bands in C6H6. Evidence is found that Coriolis coupling between some of the rotational levels of two distinct vibrational states within S1 is the mechanism responsible. This coupling mechanism is thought to be responsible for irreversible intramolecular relaxation at higher excess energies and higher vibrational state densities

Van der Waals bond lengths and electronic spectral shifts of the benzene---Kr and benzene---Xe complexes

Rotationally resolved UV-spectra are presented for the 610 bands of benzene---Kr and benzene---Xe complexes yielding precise rotational constants and van der Waals bond lengths for the ground and excited vibronic state, and electronic band shifts. These value complement the previously published data for the other rare gases and the various quantities have now been determined for all the benzene—rare gas complexes. Measured values of the bond length were used to calculate the band shifts from recent theoretical predictions. They are compared with the experimental values of this work

Doppler-free two-photon spectrum of the 000 band of the Ã1B1←X1A1 transition in difluorodiazirine, F2CN2

The Doppler-free two-photon excitation spectrum of the vibrationless Ã1B1←Image 1A1 transition of difluorodiazirine (F2CN2) has been recorded with a resolution of 15 MHz using a cw single-mode dye laser coupled to an external concentric resonator. The asymmetric rotor spectrum has been analysed and more than 350 lines randomly selected from all five branches were assigned in order to fit the ground- and excited-state rotational and quartic centrifugal distortion constants. From the rotational constants the rNN and rFF distances in the ground Image 1A1 and excited Ã1B1 state were determined. The geometry change upon excitation is found to be ΔrNN = 3.89(2) pm and ΔrFF = −4.09(2) pm. No perturbation in the rotational structure of the 000 band has been found. This points to a small singlet-triplet coupling matrix element in the small molecule limit

Frequency shifting of pulsed narrow-band laser light in a multipass Raman cell

A multipass cell is described which allows efficient stimulated Raman frequency shifting for low pump laser intensities and low gas pressures. The latter is important for Raman shifting of narrow-band Fourier-transform limited light pulses (Δv=75 MHz). It is shown that frequency broadening of the Raman shifted light can be largely avoided in the Dicke narrowing regime at low pressures. For 75 MHz pump pulses and an H2 density of 2.5 amagat we found a negligible broadening to 90 MHz of the stimulated Stokes light. This is far below the value of 250 MHz expected from spontaneous emission. The narrow-band Stokes pulses achieved in CO2 enabled us to measure the pressure shift coefficient (-0.71×10-2 cm-1/amagat) of this gas. It is demonstrated, for the example of benzene, that our technique provides a very practical light source for high resolution molecular spectroscopy

Irradiation of benzene molecules by ion-induced and light-induced intense fields

Benzene, with its sea of delocalized $\pi$-electrons in the valence orbitals, is identified as an example of a class of molecules that enable establishment of the correspondence between intense ion-induced and laser-light-induced fields in experiments that probe ionization dynamics in temporal regimes spanning the attosecond and picosecond ranges.Comment: 4 ps figure

The structure of the carbazole-(Ar)2 trimer from high resolution UV spectroscopy

Highly resolved spectra of the 000 (S1 from S0) transition of the carbazole-Ar2 complex were measured by mass-selective resonance-enhanced two-photon ionization with a narrow-band pulsed laser (delta ny < 140 MHz). The parallel c-type rotational band structure displays regular sharp features which are used to find an accurate set of rotational constants of the trimer. From the experimental result a (2 | 0) structure of the investigated complex with the two Ar atoms located on one side of the carbazole plane can be excluded. Two possible (1 | 1) structures and consequences for the solvation mechanism are discussed

High resolution UV spectroscopy of vibronic bands in p-difluorobenzene and p-difluorobenzene-Ar. The role of Herzberg-Teller coupling

Rotationally resolved spectra of two bands in the S1 from S0 transition of the p-difluorobenzene molecule and its van der Waals complex with Ar have been measured by mass-selective resonance-enhanced two-photon ionization. The rotational structure of the 000 and the 27 1 0 bands in the monomer as well as in the complex differ from each other. They can be theoretically reproduced assuming a transition moment oriented along the short in-plane axis of the molecule in the case of the 000 transition and the long in-plane axis in the case of the 27 1 0 transition. Since the magnitude of the moments of inertia is changed in the complex by adding an Ar atom, complexation leads to a change of rotational structures of the same band. The analysis of the rotational structure points to Herzberg-Teller coupling by vibronic interaction with the S2 (1B(1u)) state as the mechanism responsible for the appearance of the 27 1 0 band. The rotational constants determined from a fit of the spectra yield an e ffective van der Waals distance of 3.55 (2) A.U. (1 A.U. = 10(exp -10) m) of the Ar atom from the p-difluorobenzene plane, which decreases by 0.06 A.U. on electronic excitation to the S1 state