Invitation to a talk by Bryan Changala, JILA, University of Colorado, Boulder

20.04.2018 11:15 - 12:00

Infrared frequency combs for high resolution spectroscopy of large buffer gas cooled molecules

Friday, April 20th, 2018, 11:15 a.m.

Infrared frequency combs for high resolution

spectroscopy of large buffer gas cooled molecules

Infrared spectroscopy is a primary tool for investigating molecular structure and nuclear motion

dynamics. Extraordinarily precise and detailed insights are achievable when experiments reach

"rotational resolution," i.e. when transition frequencies between internal rotation-vibration (and even

hyperfine) states of a molecule are individually resolved, permitting the determination of the effective

molecular Hamiltonian. The experimental feasibility of this task depends strongly on molecule size and

atom number: large molecules have numerous degrees of freedom, and thermally access many internal

quantum states at standard conditions – all resulting in dense, congested spectra.

Addressing these issues requires both a sensitive, high resolution spectrometer and a method to prepare

cold molecular gases of sufficient number density. In our group, the first need is met with infrared

frequency combs coupled to high finesse enhancement cavities for direct broadband absorption

spectroscopy. These combs utilize a variety of technologies, including optical parametric oscillator and

difference frequency generation based sources. In particular, I will discuss the current development of

long wavelength comb systems extending to and beyond 10 μm. Secondly, we prepare cold gas-phase

molecules using the technique of buffer gas collisional cooling, wherein a cyrogenically cooled inert

buffer gas is used to thermalize hot molecular samples to lower than 10 K. I will present several

applications of this method to a variety of complex molecular systems, culminating in our most recent

results on the cooling and first rotationally resolved spectrum of buckminsterfullerene, C

Seminar room, 3rd floor, Boltzmanngasse 5, 1090 Vienna