Collisional relaxation of vibrational states of SrOH with He at 2K

Vibrational relaxation of strontium monohydroxide (SrOH) molecules in collisions with helium (He) at 2K is studied. We find the diffusion cross section of SrOH at 2.2 K to be sigma(d) = (5 +/- 2) x 10(-14) cm(2) and the vibrational quenching cross section for the (100) Sr-O stretching mode to be sigma(q) = (7 +/- 2) x 10(-17) cm(2). The resulting ratio gamma(100) = sigma(d)/sigma(q) similar to 700 is more than an order of magnitude smaller than for previously studied few-atom radicals (Au et al 2014 Phys. Rev. A90 032703). We also determine the Franck-Condon factor for SrOH ((A) over tilde (2) Pi(1/2) (100) <- (X) over tilde (2) Sigma(+) (000)) to be (4.8 +/- 0.8) x 10(-2).