Two-proton laser spectroscopy of small molecules

• Main Author: Zhiyuan, M.
• Published: University of Edinburgh 1997
• Subjects: 541.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664235

An innovative optical-optical double resonance scheme (bound-free-bound) which employs resonant continuum intermediate states has been developed. A full quantum explanation has been suggested for the development of the vibronic envelope of the final states excited through such bound-free-bound pathways with two-colour pulsed layers. This scheme has been applied to observing extended vibrational progressions of some 0<SUP>+</SUP><SUB>g</SUB> and 1<SUB>g</SUB> ion-pair states of I<SUB>2</SUB> and C1<SUB>2</SUB>, and the [<SUP>2</SUP>II<SUB>1/2</SUB>]6s;0 Rydberg state of methyl iodide (along the C-I stretching mode, <I>v</I><SUB>3</SUB>). The vibrational structures of the E0<SUP>+</SUP><SUB>g</SUB> and f0<SUP>+</SUP><SUB>g</SUB> ion-pair states of I<SUB>2</SUB> are simulated by using the resultant Franck-Condon calculation. The vibrational structure of the 0<SUP>+</SUP><SUB>g</SUB> and 1<SUB>g</SUB> ion-pair states of C1<SUB>2</SUB> also agrees with the predictions from the Franck-Condon calculations. The curtailment at <I>v</I><SUP>1</SUP> = 5 of the <I>v</I><SUB>3</SUB> vibrational progression of the methyl iodide [<SUP>2</SUP>II<SUB>1/2</SUB>]6s;0 Rydberg state has been attributed to the sudden onset of predissociation. The two-photon Hönl-London factors for (a) a well defined intermediate (<I>J<SUB>i</SUB>, M<SUB>i</SUB>),</I> (b) a coherently superposed (<I>J<SUB>i</SUB>, M<SUB>i</SUB></I>) and (c) a full set of coherent virtual states, are discussed. The simulation of the observed rotational contours of the 0<SUP>+</SUP><SUB>g</SUB> ion-pair states of I<SUB>2</SUB> and C1<SUB>2</SUB> in the bound-free-bound scheme reveals the dominant character of the intermediate electronic states. Similar deductions cannot be made for the 1<SUB>g</SUB> ion-pair states of C1<SUB>2</SUB> and the reason is discussed. The two-colour two-photon nonresonant excitation of the 0<SUP>0</SUP><SUB>0</SUB> vibronic band of the (<SUP>2</SUP><I>A"<SUB>2</SUB></I>)3p<I><SUB>z</SUB></I> Rydberg state of CD<SUB>3</SUB> has been observed and its rotational contour has also been simulated on the basis of established Hönl-London factors. The dynamics of the virtual intermediate states can be revealed by considering the observed parallel and perpendicular polarization spectra. A relative resonant enhancement of the 2<SUP>1</SUP><SUB>3</SUB> vibronic band of the (<SUP>2</SUP><I>A<SUP>11</SUP><SUB>2</SUB>)</I>4p<I><SUB>z</SUB></I> Rydberg state, in the out-of-plane mode (<I>v</I><SUB>2</SUB>), occurred when the protons were turned on and off resonances with the intermediate (<SUP>2</SUP><I>A<SUP>1</SUP><SUB>1</SUB></I>)3s state which is strongly predissocated by tunnelling.