Issue 35, 2015

Roaming as the dominant mechanism for molecular products in the photodissociation of large aliphatic aldehydes

Abstract

Photodissociation of isobutyraldehyde (C3H7CHO) at 248 nm is investigated using time-resolved Fourier-transform infrared emission spectroscopy to demonstrate the growing importance of the roaming pathway with increasing molecular size of aliphatic aldehydes. Each acquired CO rotational distribution from v = 1 to 4 is well characterized by a single Boltzmann rotational temperature from 637 to 750 K, corresponding to an average rotational energy of 5.9 ± 0.6 kJ mol−1. The roaming signature that shows a small fraction of CO rotational energy disposal accompanied by a vibrationally hot C3H8 co-fragment is supported by theoretical prediction. The energy difference between the tight transition state (TS) and the roaming saddle point (SP) is found to be −27, 4, 15, 22, and 30 kJ mol−1 for formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, and 2,2-dimethyl propanal, respectively. The roaming SP is stabilized by a larger alkyl moiety. It is suggested that the roaming photodissociation rate of aldehydes increasingly exceeds those via the tight TS, resulting in the dominance of the CO + alkane products, as the size of aldehydes becomes larger. Along with formaldehyde, acetaldehyde, and propionaldehyde, in this work isobutyraldehyde is further demonstrated that this aldehyde family with special functional group is the first case in the organic compound to follow predominantly a roaming dissociation pathway, as the molecular size becomes larger.

Graphical abstract: Roaming as the dominant mechanism for molecular products in the photodissociation of large aliphatic aldehydes

Supplementary files

Article information

Article type
Paper
Submitted
12 Jun 2015
Accepted
05 Aug 2015
First published
07 Aug 2015

Phys. Chem. Chem. Phys., 2015,17, 23112-23120

Author version available

Roaming as the dominant mechanism for molecular products in the photodissociation of large aliphatic aldehydes

P. Tsai, H. Li, T. Kasai and K. Lin, Phys. Chem. Chem. Phys., 2015, 17, 23112 DOI: 10.1039/C5CP03408F

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements