This 10th Anniversary article is written by Richard Zare, Andrew Alexander, Peter Rakitzis and colleagues. 

Richard Zare is the Marguerite Blake Wilbur Professor in Natural Science at Stanford University. He is renowned in the area of lasers applied to chemical reactions and to chemical analysis. Professor Zare is the recipient of many awards including the National Medal of Science (1983), the Welch Award in Chemistry (1999), and the Wolf Prize in Chemistry (2005). He is also a member of the PCCP Honorary Board. 

In this article, Zare and colleagues investigate the time-dependent depolarization of aligned HD molecules. 'In molecular hydrogen, nuclear spin plays a profound role,' explained Zare. 'For para-H2, I = 0, spin degeneracy = 1, the nuclear spin wavefunction is antisymmetric, and J is even, whereas for ortho-H2, I=1, spin degeneracy = 3, the nuclear spin wavefunction is symmetric, and J is odd. For D2 the assignments are reversed. But what about HD?' 

Zare and colleagues show that the two different spins of H and D nuclei couple to the rotational angular momentum J to cause J to precess in a complex manner about the resultant total angular momentum of the molecular system. 'This behaviour can have consequences for scattering experiments in which the HD target is prepared in specific rotational levels,' said Zare. 

The researchers chose to publish their work in PCCP because of the wide international readership of the journal. 

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