We describe an advanced undergraduate experiment to demonstrate molecular spectroscopy by measuring the vibrational energy spacing of nitrogen molecules in the gas phase. We show how the use of a simple and readily available AC discharge tube and a handheld spectrometer allows students to observe and measure the radiative collisional phenomena in the gas, and to scrutinize the resulting emission spectrum for an instructive analysis of the quantized vibrational potential of neutral as well as ionized N2.

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An upper-division laboratory course in atomic and molecular spectroscopy is described. Examples of outcomes that also benefit second-year physics laboratories and demonstrations in introductory courses are presented. The overarching goal that drove the development of the course was to assist students in understanding the fundamental connections between atomic and molecular spectra and the underlying structures. A selection of laboratory experiences supporting this goal, and the equipment and techniques necessary to provide them, are outlined.

We have narrowed the spectral bandwidth of a commercial 2 W laser diode array to be less than 120 MHz near 780 nm. The external-cavity laser diode array system is a standard double-pass Littman-Metcalf configuration operating on a dominant single longitudinal mode.

We present in this paper results of a nonlinear optical spectroscopy approach to measurement of excited-state transition matrix elements. Recent advances in the quality of excited-state transition matrix elements have permitted renormalization of earlier measurements of transition amplitudes associated with the 5s 2S1/2 → 5p 2Pj → 5d 2D3/2 two-photon transitions in atomic 87Rb. Previous measurements were made to high precision, but further improvement of the accuracy was limited by uncertainties in data describing the influence of energetically distant transitions. Availability of more reliable matrix elements, including relativistic all-order calculations of transition matrix elements in alkali atoms, has since significantly improved the situation. In the present paper, we show that theoretical relative transition amplitudes for the excited state 5p 2Pj → 5d 2D3/2 doublet (ratio = 1.098(9)) are now in excellent agreement with experiment (ratio = 1.090(6)). This result, combined with our recent work on caesium, shows that it is possible to determine relative line strengths, for transitions connecting atomic excited states, with precision previously found only in state-of-the-art measurements of alkali resonance doublets. Detailed discussion of the experimental technique and supporting data, including polarization measurements on the 5s 2S1/2 → 5p 2Pj → 5d 2D5/2 transitions, is also presented.