RADIATIVE COOLING RATE OF 9-CYANOPHENANTHRENE IONS BY TIME-RESOLVED PHOTODISSOCIATION THERMOMETRY

Hot ions of 9-cyanophenanthrene were produced by multiphoton ionizatio n at 193 nm. The radiative cooling rate of the hot ions was measured t hermometrically using time-resolved photodissociation (TRPD) as the in ternal energy probe. In this application of the TRPD technique two-pho ton dissociation of the ions at 355 nm was used to measure the rate fo r the C2H2 loss channel as a function of cooling time following the io nization laser pulse. Since the TRPD rate depends on the ion internal energy the dissociation rate measurements gave a cooling curve for the initially hot ions. The radiative cooling time constant was measured as 330 ms. The cooling rate observed here is faster than the radiative cooling rates of comparable nonpolar ions. This enhancement of radiat ive cooling is attributed to high vibrational transition dipole moment s associated with the polar CN group.