Mass-selective rotational coherence spectroscopy by (1+1′) pump–probe photoionization

Abstract

We report the first experimental results on a simple scheme for mass-selective rotational coherence spectroscopy (RCS) employing a (1 + 1′) UV pump–probe photoionization setup. A solid state two-color UV ps laser system, optimized for high-resolution RCS, provides two independently wavelength tunable, linearly polarized output pulses. The pump pulse resonantly excites a sample and creates a superposition of rovibronic states at time zero. After a variable delay time a probe pulse, non-resonant to transitions in the neutral manifold of the sample, is applied for photoionization and the ion-yield is recorded. By this method sharp and intense J-type transients for the molecule para-cyclohexylaniline (pCHA) have been identified. Correspondingly, transients of opposite polarity have been obtained by detection of fluorescence from the first electronic excited state. The transient positions allow the determination of the excited state rotational constants of pCHA. The obtained values confirm the results of our former high-resolution fluorescence depletion RCS study of pCHA. Moreover, due to its relative simple implementation and mass-selectivity, the presented photoionization setup bears great potential for future applications in the structural analysis of molecular clusters.