Ramsey-type microwave spectroscopy on CO (α3 II)

Using a Ramsey-type setup, the lambda-doublet transition in the J = I, Omega = 1 level of the alpha(3) II state of CO was measured to be 394064870(10) Hz. In a molecular beam apparatus, a beam of metastable CO is prepared in a single quantum level by expanding CO into vacuum and exciting the molecules using a narrow-band UV laser system. After passing two microwave zones that are separated by 50 cm, the molecules are state-selectively deflected and detected 1 meter downstream on a position sensitive detector. In order to keep the molecules in a single m(J)(B) level, a magnetic bias field is applied. We find the field-free transition frequency by taking the average of the m(J)(B) = +1 -> m(J)(B) = +1 and m(J)(B) = 1 -> m(J)(B) = 1 transitions, which have an almost equal but opposite Zeeman shift. The accuracy of this proof-of-principle experiment is a factor of 100 more accurate than the previous best value obtained for this transition. (C) 2014 Elsevier Inc. All rights reserved.